/* === CSS Variables & Theme === */
:root {
    --bg-primary: #0a0a0f;
    --bg-secondary: #12121a;
    --bg-tertiary: #1a1a25;
    --bg-hover: #22222f;
    --border-color: #2a2a3a;
    --border-glow: rgba(0, 245, 212, 0.3);
    
    --text-primary: #f0f0f5;
    --text-secondary: #a0a0b0;
    --text-muted: #606070;
    
    --accent-cyan: #00f5d4;
    --accent-purple: #9b5de5;
    --accent-pink: #f15bb5;
    --accent-yellow: #fee440;
    
    --gradient-main: linear-gradient(135deg, var(--accent-cyan), var(--accent-purple));
    
    --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.3);
    --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.4);
    --shadow-glow: 0 0 20px rgba(0, 245, 212, 0.15);
    
    --radius-sm: 6px;
    --radius-md: 10px;
    --radius-lg: 16px;
    
    --font-sans: 'Outfit', -apple-system, BlinkMacSystemFont, sans-serif;
    --font-mono: 'JetBrains Mono', 'Fira Code', monospace;
    
    --transition-fast: 0.15s ease;
    --transition-normal: 0.25s ease;
}

/* === Reset & Base === */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html, body {
    height: 100%;
    overflow: hidden;
}

body {
    font-family: var(--font-sans);
    background: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.5;
    -webkit-font-smoothing: antialiased;
}

/* === App Layout === */
#app {
    display: flex;
    flex-direction: column;
    height: 100vh;
    background: 
        radial-gradient(ellipse at 20% 20%, rgba(155, 93, 229, 0.08) 0%, transparent 50%),
        radial-gradient(ellipse at 80% 80%, rgba(0, 245, 212, 0.06) 0%, transparent 50%),
        var(--bg-primary);
}

/* === Header === */
.header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0.75rem 1.5rem;
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border-color);
    z-index: 100;
}

.logo {
    display: flex;
    align-items: center;
    gap: 0.75rem;
}

.logo-icon {
    width: 32px;
    height: 32px;
}

.logo-text {
    font-size: 1.25rem;
    font-weight: 600;
    background: var(--gradient-main);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    letter-spacing: -0.02em;
}

.header-controls {
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.unsaved-indicator:not([hidden]) {
    color: var(--accent-yellow);
    font-size: 0.72rem;
    white-space: nowrap;
}

/* Edit toggle: one button, off = measure (the safe default), on = edit */
.mode-btn {
    display: flex;
    align-items: center;
    gap: 0.4rem;
    padding: 0.5rem 0.75rem;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    background: var(--bg-tertiary);
    color: var(--text-secondary);
    font-size: 0.8rem;
    font-family: var(--font-sans);
    cursor: pointer;
    transition: all var(--transition-fast);
}

.mode-btn:hover {
    color: var(--text-primary);
    background: var(--bg-hover);
    border-color: var(--accent-pink);
}

.mode-btn.active[data-mode="edit"] {
    background: rgba(241, 91, 181, 0.2);
    border-color: var(--accent-pink);
    color: var(--accent-pink);
}

.mode-btn svg {
    opacity: 0.8;
}

.mode-btn.active svg {
    opacity: 1;
}

.header-separator {
    width: 1px;
    height: 24px;
    background: var(--border-color);
    margin: 0 0.25rem;
}

/* === Buttons === */
.btn {
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 0.5rem 0.75rem;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    background: var(--bg-tertiary);
    color: var(--text-secondary);
    cursor: pointer;
    transition: all var(--transition-fast);
}

.btn:hover {
    background: var(--bg-hover);
    color: var(--text-primary);
    border-color: var(--accent-cyan);
}

.btn.active {
    background: rgba(0, 245, 212, 0.15);
    border-color: var(--accent-cyan);
    color: var(--accent-cyan);
}

/* Toolbar buttons that carry a word beside their icon */
.btn-labelled {
    gap: 0.4rem;
    font-size: 0.8rem;
    font-family: var(--font-sans);
    white-space: nowrap;
}

/* Reset View lives on the 3D view, since it is about the camera, not the
   document. It is page chrome over the canvas and never part of an export. */
.viewport-reset {
    position: absolute;
    top: 0.75rem;
    right: 0.75rem;
    z-index: 10;
    display: flex;
    align-items: center;
    gap: 0.35rem;
    padding: 0.35rem 0.65rem;
    border: 1px solid var(--border-color);
    border-radius: 999px;
    background: rgba(20, 20, 30, 0.72);
    color: var(--text-secondary);
    font-size: 0.75rem;
    font-family: var(--font-sans);
    cursor: pointer;
    backdrop-filter: blur(4px);
    transition: all var(--transition-fast);
}

.viewport-reset:hover {
    color: var(--text-primary);
    border-color: var(--accent-cyan);
    background: rgba(20, 20, 30, 0.9);
}

.viewport-reset[hidden] {
    display: none;
}

body.light-scene .viewport-reset {
    background: rgba(255, 255, 255, 0.78);
    color: #16161d;
    border-color: rgba(22, 22, 29, 0.25);
}

/* === Main Content === */
.main-content {
    display: flex;
    flex: 1;
    overflow: hidden;
}

/* === Sidebar === */
.sidebar {
    container-type: inline-size;
    container-name: sidebar;
    width: var(--sidebar-width, 280px);
    min-width: 0;
    flex-shrink: 0;
    background: var(--bg-secondary);
    border-right: 1px solid var(--border-color);
    display: flex;
    flex-direction: column;
    overflow-y: auto;
}

.panel {
    padding: 1rem 1.25rem;
    border-bottom: 1px solid var(--border-color);
}

.panel-title {
    font-size: 0.75rem;
    font-weight: 500;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--text-muted);
    margin-bottom: 0.75rem;
}

.placeholder-text {
    color: var(--text-muted);
    font-size: 0.875rem;
    font-style: italic;
}

/* === Structure Info === */
.info-content {
    font-family: var(--font-mono);
    font-size: 0.8rem;
}

.info-item {
    display: flex;
    justify-content: space-between;
    padding: 0.35rem 0;
    border-bottom: 1px solid rgba(255, 255, 255, 0.05);
}

.info-item:last-child {
    border-bottom: none;
}

.info-label {
    flex-shrink: 0;
    margin-right: .75rem;
    color: var(--text-secondary);
}

.info-value {
    min-width: 0;
    overflow-wrap: anywhere;
    text-align: right;
    color: var(--accent-cyan);
    font-weight: 500;
}

/* === Atom List === */
/* The species list and the atom-number control grow with their content; the
   sidebar as a whole scrolls, so nothing is clipped inside the panel. */
.atom-list-content {
    overflow: visible;
}

.atom-entry {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    padding: 0.5rem;
    border-radius: var(--radius-sm);
    transition: background var(--transition-fast);
}

.atom-entry:hover {
    background: var(--bg-hover);
}

.atom-sphere {
    width: 24px;
    height: 24px;
    border-radius: 50%;
    box-shadow: 
        inset -3px -3px 6px rgba(0, 0, 0, 0.4),
        inset 3px 3px 6px rgba(255, 255, 255, 0.2),
        var(--shadow-sm);
}

.atom-info {
    flex: 1;
}

.atom-symbol {
    font-weight: 600;
    font-size: 0.95rem;
}

.atom-count {
    font-size: 0.75rem;
    color: var(--text-muted);
    font-family: var(--font-mono);
}

.atom-jump-form {
    padding: 0.75rem 0.5rem 0.2rem;
    border-top: 1px solid var(--border-color);
}

.atom-jump-form label,
.exact-atom-section > label {
    display: block;
    margin-bottom: 0.4rem;
    color: var(--text-secondary);
    font-size: 0.75rem;
}

.atom-jump-row {
    display: flex;
    gap: 0.4rem;
}

.atom-jump-row input {
    min-width: 0;
    flex: 1;
    padding: 0.4rem;
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    color: var(--text-primary);
    font-family: var(--font-mono);
}

.atom-jump-row input:focus-visible {
    outline: 2px solid var(--accent-cyan);
}

.exact-atom-section {
    margin: 0.8rem 0;
    padding: 0.75rem;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    background: var(--bg-tertiary);
}

.exact-atom-section .element-select {
    width: 100%;
    margin-bottom: 0.65rem;
}

/* Dragging creates precise values; keep the complete number readable at
   the current sidebar width instead of squeezing three fields into one row. */
.exact-atom-section .add-atom-coords {
    flex-wrap: wrap;
}

.exact-atom-section .coord-input-group {
    flex: 1 1 9rem;
    min-width: 0;
}

.exact-atom-section .btn {
    width: 100%;
}

/* Arrow step of the coordinate fields */
.coord-step-row {
    display: flex;
    align-items: center;
    gap: 0.35rem;
    margin-bottom: 0.65rem;
}

.coord-step-label {
    font-size: 0.75rem;
    color: var(--text-muted);
    margin-right: 0.15rem;
}

.coord-step {
    flex: 1;
    padding: 0.25rem 0.4rem;
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    color: var(--text-secondary);
    font-family: var(--font-mono);
    font-size: 0.75rem;
    cursor: pointer;
    transition: background 0.15s, border-color 0.15s, color 0.15s;
}

.coord-step:hover {
    border-color: var(--text-muted);
}

.coord-step[aria-pressed="true"] {
    background: rgba(0, 245, 212, 0.15);
    border-color: var(--accent-cyan);
    color: var(--accent-cyan);
}

.coord-step:focus-visible {
    outline: 2px solid var(--accent-cyan);
    outline-offset: 1px;
}

.coord-edit-hint {
    font-size: 0.7rem;
    color: var(--text-muted);
    text-align: center;
}

/* === Controls Panel === */
.control-group {
    margin-bottom: 1rem;
}

.control-group:last-child {
    margin-bottom: 0;
}

.control-group label {
    display: block;
    font-size: 0.8rem;
    color: var(--text-secondary);
    margin-bottom: 0.4rem;
}

.control-group input[type="range"] {
    width: 100%;
    height: 6px;
    border-radius: 3px;
    background: var(--bg-tertiary);
    appearance: none;
    cursor: pointer;
}

.control-group input[type="range"]::-webkit-slider-thumb {
    appearance: none;
    width: 16px;
    height: 16px;
    border-radius: 50%;
    background: var(--accent-cyan);
    cursor: pointer;
    box-shadow: 0 0 10px rgba(0, 245, 212, 0.5);
    transition: transform var(--transition-fast);
}

.control-group input[type="range"]::-webkit-slider-thumb:hover {
    transform: scale(1.2);
}

.value-display {
    font-family: var(--font-mono);
    font-size: 0.75rem;
    color: var(--accent-cyan);
    float: right;
    margin-top: -2rem;
}

.checkbox-group label {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    cursor: pointer;
}

.checkbox-group input[type="checkbox"] {
    width: 16px;
    height: 16px;
    accent-color: var(--accent-cyan);
    cursor: pointer;
}

/* === Measurement Panel === */
/* The mode panel carries a stripe in the mode's colour: cyan for Measure,
   the canvas glow's coral for Edit. The Display panel below stays neutral. */
.measurement-panel {
    background: none;
    border-left: 3px solid var(--accent-cyan);
    padding-left: calc(1.25rem - 3px);
}

body.edit-mode-active .measurement-panel {
    border-left-color: #ff6b6b;
}

.measurement-content {
    min-height: 60px;
}

.selected-atoms {
    display: flex;
    flex-direction: column;
    gap: 0.4rem;
    margin-bottom: 1rem;
}

.selected-atom {
    display: flex;
    align-items: center;
    flex-wrap: wrap;
    gap: 0.5rem;
    padding: 0.4rem 0.6rem;
    background: var(--bg-tertiary);
    border-radius: var(--radius-sm);
    position: relative;
    overflow: hidden;
}

.selected-atom .color-strip {
    position: absolute;
    left: 0;
    top: 0;
    bottom: 0;
    width: 4px;
}

.sel-num {
    width: 22px;
    height: 22px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.75rem;
    font-weight: 700;
    color: #000;
    margin-left: 0.25rem;
}

.selected-atoms-more {
    font-size: 0.75rem;
    color: var(--text-muted);
    text-align: center;
    padding: 0.3rem 0 0.1rem;
}

.sel-elem {
    font-weight: 600;
    font-size: 0.95rem;
}

.sel-idx {
    font-family: var(--font-mono);
    font-size: 0.75rem;
    color: var(--text-muted);
    margin-left: auto;
}

.sel-coords {
    width: 100%;
    font-family: var(--font-mono);
    font-size: 0.7rem;
    margin-top: 0.25rem;
    padding-left: 2.5rem;
    opacity: 0.85;
}

button.sel-coords,
button.meas-delta {
    appearance: none;
    background: transparent;
    border-left: 0;
    border-right: 0;
    border-bottom: 0;
    text-align: left;
    cursor: pointer;
}

button.sel-coords {
    border-top: 0;
    padding-top: 0;
    padding-right: 0;
    padding-bottom: 0;
}

button.meas-delta {
    padding-left: 0;
    padding-right: 0;
}

button.sel-coords:focus-visible,
button.meas-delta:focus-visible {
    outline: 2px solid var(--accent-cyan);
    outline-offset: 2px;
}

/* Clickable coordinates - toggle between fractional/cartesian */
.clickable-coords {
    cursor: pointer;
    transition: opacity var(--transition-fast);
}

.clickable-coords:hover {
    opacity: 1;
}

/* Fractional coordinates - gold/yellow with square brackets */
.sel-coords-frac {
    color: var(--accent-yellow);
}

/* Cartesian coordinates - cyan with parentheses */
.sel-coords-cart {
    color: var(--accent-cyan);
}

.measurement-result {
    display: flex;
    align-items: stretch;
    background: var(--bg-tertiary);
    border-radius: var(--radius-sm);
    margin-bottom: 0.5rem;
    overflow: hidden;
}

/* Multi-color strip for measurements */
.multi-color-strip {
    display: flex;
    flex-direction: column;
    width: 6px;
    flex-shrink: 0;
}

.multi-color-strip .strip-segment {
    flex: 1;
}

.multi-color-strip.triple .strip-segment {
    flex: 1;
}

.meas-content {
    flex: 1;
    min-width: 0;
    gap: 0.3rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0.6rem 0.75rem;
}

.meas-label {
    font-size: 0.8rem;
    color: var(--text-secondary);
}

.meas-value {
    max-width: 100%;
    overflow-wrap: anywhere;
    font-family: var(--font-mono);
    font-size: 0.95rem;
    font-weight: 600;
    color: var(--text-primary);
}

.meas-value.angle-value {
    color: var(--text-primary); /* White, not yellow - avoids confusion with selection color */
}

/* Delta display under distance measurements (unified fractional/cartesian) */
.meas-delta {
    display: flex;
    flex-wrap: wrap;
    gap: 0.25rem;
    width: 100%;
    margin-top: 0.35rem;
    padding-top: 0.3rem;
    border-top: 1px solid rgba(255, 255, 255, 0.06);
    font-family: var(--font-mono);
    font-size: 0.7rem;
    color: var(--text-muted);
}

.delta-item {
    display: flex;
    align-items: center;
    gap: 0.15rem;
    flex: 1 1 70px;
}

.delta-label {
    font-size: 0.6rem;
    font-weight: 600;
    padding: 0.05rem 0.2rem;
    border-radius: 3px;
    flex-shrink: 0;
}

.delta-label.delta-a {
    background: rgba(255, 107, 107, 0.2);
    color: #ff6b6b;
}

.delta-label.delta-b {
    background: rgba(105, 240, 174, 0.2);
    color: #69f0ae;
}

.delta-label.delta-c {
    background: rgba(100, 181, 246, 0.2);
    color: #64b5f6;
}

/* Clickable delta row - cursor and hover feedback */
.clickable-delta {
    cursor: pointer;
    transition: opacity var(--transition-fast);
}

.clickable-delta:hover {
    opacity: 1 !important;
}

/* Fractional mode: yellow values (matching atom coord color) */
.meas-delta.delta-frac {
    color: var(--accent-yellow);
}

/* Cartesian mode: cyan values (matching atom coord color) */
.meas-delta.delta-cart {
    color: var(--accent-cyan);
}

/* Make meas-content wrap for the delta sub-row */
.meas-content {
    flex-wrap: wrap;
}

.btn-clear {
    width: 100%;
    margin-top: 0.75rem;
    padding: 0.6rem;
    background: transparent;
    border: 1px dashed var(--border-color);
    color: var(--text-secondary);
    font-size: 0.8rem;
    transition: all var(--transition-fast);
}

.btn-clear:hover {
    border-color: var(--accent-pink);
    color: var(--accent-pink);
    background: rgba(241, 91, 181, 0.1);
}

/* Edit Mode Styles */
.edit-warning {
    margin-bottom: 0.5rem;
    font-size: 0.8rem;
    color: var(--text-secondary);
}

/* Live measurement readout in Edit mode: one flat row per measurement under
   the instruction line, carrying the Measurements panel's colour stripe. The
   full view (atoms, coordinates, displacements) stays in that panel. */
.measurement-readouts {
    display: flex;
    flex-direction: column;
    margin: 0.25rem 0 0.75rem;
    border-top: 1px solid var(--border-color);
    border-bottom: 1px solid var(--border-color);
}

.measurement-readout {
    display: flex;
    align-items: center;
    gap: 0.6rem;
    padding: 0.45rem 0;
}

.measurement-readout + .measurement-readout {
    border-top: 1px solid var(--border-color);
}

.measurement-readout .multi-color-strip {
    width: 3px;
    align-self: stretch;
    min-height: 1.1rem;
    border-radius: 2px;
    overflow: hidden;
}

.measurement-readout .readout-body {
    flex: 1;
    min-width: 0;
    display: flex;
    flex-wrap: wrap;
    align-items: baseline;
    gap: 0.15rem 0.75rem;
}

.readout-item {
    display: inline-flex;
    align-items: baseline;
    gap: 0.3rem;
    white-space: nowrap;
}

.readout-label {
    font-size: 0.7rem;
    color: var(--text-secondary);
}

.readout-value {
    font-family: var(--font-mono);
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--text-primary);
}

.readout-hint {
    font-size: 0.75rem;
    color: var(--text-muted);
    white-space: normal;
}

.measurement-readout .readout-clear {
    flex-shrink: 0;
}

.selected-atom.edit .color-strip {
    background: var(--accent-cyan) !important;
}

.selected-atom.edit {
    border: 1px solid var(--border-color);
}

.btn-delete {
    width: 100%;
    padding: 0.7rem;
    background: rgba(255, 80, 80, 0.2);
    border: 1px solid #ff5050;
    color: #ff5050;
    font-size: 0.85rem;
    font-weight: 500;
    transition: all var(--transition-fast);
    margin-bottom: 0.5rem;
}

.btn-delete:hover {
    background: #ff5050;
    color: #000;
}

.btn-undo {
    width: 100%;
    margin-top: 0.5rem;
    padding: 0.6rem;
    background: rgba(254, 228, 64, 0.1);
    border: 1px solid rgba(254, 228, 64, 0.5);
    color: var(--accent-yellow);
    font-size: 0.8rem;
    transition: all var(--transition-fast);
}

.btn-undo:hover {
    background: rgba(254, 228, 64, 0.2);
    border-color: var(--accent-yellow);
}

.edit-instructions {
    font-size: 0.75rem;
    color: var(--text-muted);
    text-align: center;
    padding: 0 0 0.25rem;
    margin-bottom: 0.5rem;
}

.undo-section {
    display: flex;
    flex-direction: column;
    gap: 0.4rem;
    margin-top: 0.75rem;
    padding-top: 0.75rem;
    border-top: 1px dashed var(--border-color);
}

/* Edit mode active indicator */
body.edit-mode-active .viewport {
    box-shadow: inset 0 0 0 2px rgba(255, 80, 80, 0.3);
}


/* === Viewport === */
.viewport-container {
    min-width: 0;
    flex: 1;
    display: flex;
    flex-direction: column;
    position: relative;
    overflow: hidden;
    background: var(--bg-primary);
    container-type: inline-size;
}

.viewport {
    position: relative;
    width: 100%;
    flex: 1;
    min-height: 0;
    background: 
        radial-gradient(circle at center, var(--bg-tertiary) 0%, var(--bg-primary) 100%);
}

.viewport canvas {
    display: block;
}

/* === Drop Zone === */
.drop-zone {
    position: absolute;
    inset: 0;
    overflow: hidden;
    background: rgba(10, 10, 15, 0.95);
    z-index: 50;
    cursor: default;
    transition: all var(--transition-normal);
}

/* Scroll the picker content independently of its anchored close control. */
.drop-zone-scroll {
    width: 100%;
    height: 100%;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: flex-start;
    gap: 1rem;
    padding: 1.25rem 1.5rem;
    overflow: auto;
    box-sizing: border-box;
}

.drop-zone-close {
    position: absolute;
    top: 0.75rem;
    right: 0.75rem;
    width: 32px;
    height: 32px;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    background: var(--bg-tertiary);
    color: var(--text-secondary);
    font-size: 1.25rem;
    line-height: 1;
    cursor: pointer;
    z-index: 1;
}

.drop-zone-close:hover {
    color: var(--text-primary);
    border-color: var(--accent-cyan);
}

.drop-zone-close.hidden {
    display: none;
}

.drop-zone.hidden {
    display: none;
}

.drop-zone.drag-over {
    background: rgba(0, 245, 212, 0.1);
}

.drop-zone.drag-over .drop-zone-content {
    transform: scale(1.05);
}

.drop-zone.drag-over .drop-icon {
    color: var(--accent-cyan);
}

.drop-zone-content {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 0.35rem;
    cursor: pointer;
    transition: transform var(--transition-normal);
    flex-shrink: 0;
    /* Auto margins center fitting content, but collapse to zero when the
       picker overflows so its beginning remains reachable by scrolling. */
    margin-top: auto;
}

.example-picker {
    width: min(560px, 100%);
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
    margin-bottom: auto;
}

.example-picker-title {
    text-align: center;
    font-size: 0.8rem;
    letter-spacing: 0.08em;
    text-transform: uppercase;
    color: var(--text-muted);
}

.example-list {
    display: flex;
    flex-direction: column;
    gap: 0.85rem;
}

.example-group-label {
    font-size: 0.7rem;
    font-weight: 600;
    letter-spacing: 0.08em;
    text-transform: uppercase;
    color: var(--text-secondary);
    margin-bottom: 0.4rem;
}

.example-group-buttons {
    display: flex;
    flex-wrap: wrap;
    gap: 0.4rem;
}

.example-chip {
    display: inline-flex;
    flex-direction: column;
    align-items: flex-start;
    gap: 0.1rem;
    padding: 0.35rem 0.6rem;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    background: var(--bg-tertiary);
    color: var(--text-primary);
    cursor: pointer;
    text-align: left;
    transition: all var(--transition-fast);
}

.example-chip:hover {
    border-color: var(--accent-cyan);
    background: var(--bg-hover);
    color: var(--accent-cyan);
}

.example-chip-title {
    font-size: 0.8rem;
    font-weight: 500;
}

.example-chip-meta {
    font-size: 0.65rem;
    color: var(--text-muted);
    font-family: var(--font-mono);
}

.drop-icon {
    width: 40px;
    height: 40px;
    color: var(--text-muted);
    transition: color var(--transition-normal);
}

.drop-text {
    font-size: 1rem;
    font-weight: 500;
    color: var(--text-primary);
}

.drop-subtext {
    font-size: 0.875rem;
    color: var(--text-muted);
}

/* Reserve navigation-help space so fitting and pointer projection use
   an unobstructed canvas, including after panel/window changes. */
.viewport-guidance {
    flex: 0 0 auto;
    display: flex;
    justify-content: center;
    padding: 0 1rem 1rem;
    pointer-events: none;
    z-index: 10;
}

.controls-hint {
    display: flex;
    gap: 1.5rem;
    padding: 0.5rem 1rem;
    background: rgba(18, 18, 26, 0.9);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    backdrop-filter: blur(10px);
}

.controls-hint span {
    font-size: 0.75rem;
    color: var(--text-secondary);
    white-space: nowrap;
}

/* Sidebar resizing changes the viewer without changing the window width. */
@container (max-width: 640px) {
    .viewport-guidance {
        display: none;
    }
}

/* === Status Bar === */
.status-left {
    flex: 1;
    min-width: 0;
    overflow-wrap: anywhere;
}
.status-right {
    flex-shrink: 0;
    white-space: nowrap;
}

.status-bar {
    display: flex;
    justify-content: space-between;
    gap: 0.75rem;
    padding: 0.4rem 1rem;
    background: var(--bg-secondary);
    border-top: 1px solid var(--border-color);
    font-size: 0.75rem;
    font-family: var(--font-mono);
    color: var(--text-muted);
}

@media (max-width: 480px) {
    .status-bar {
        flex-direction: column;
        gap: 0.25rem;
    }
}

#statusText.success {
    color: var(--accent-cyan);
}

#statusText.error {
    color: var(--accent-pink);
}

#statusText.warning,
.geometry-warning,
.info-warning {
    color: var(--accent-yellow);
}

.geometry-warning:not([hidden]) {
    display: block;
    margin-top: 0.25rem;
    max-width: 70ch;
    line-height: 1.4;
}

.info-warning {
    margin-top: 0.75rem;
    font-size: 0.75rem;
    line-height: 1.4;
}

/* === Scrollbar === */
::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}

::-webkit-scrollbar-track {
    background: var(--bg-primary);
}

::-webkit-scrollbar-thumb {
    background: var(--bg-hover);
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: var(--border-color);
}

/* === Periodic Images Controls === */
.periodic-group {
    display: flex;
    flex-direction: column;
    gap: 0.6rem;
}

.periodic-group.disabled {
    opacity: 0.45;
}

.btn:disabled, .stepper-btn:disabled {
    opacity: 0.45;
    cursor: not-allowed;
}

.stepper-btn:disabled:hover {
    background: transparent;
    color: var(--text-secondary);
}

.periodic-row {
    display: flex;
    flex-wrap: wrap;
    justify-content: space-between;
    gap: 0.4rem;
}

.periodic-axis {
    min-width: 74px;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 0.4rem;
    flex: 1;
}

.axis-badge {
    font-family: var(--font-mono);
    font-size: 0.7rem;
    font-weight: 600;
    padding: 0.15rem 0.5rem;
    border-radius: 10px;
}

.axis-badge.axis-a {
    background: rgba(255, 107, 107, 0.2);
    color: #ff6b6b;
}

.axis-badge.axis-b {
    background: rgba(105, 240, 174, 0.2);
    color: #69f0ae;
}

.axis-badge.axis-c {
    background: rgba(100, 181, 246, 0.2);
    color: #64b5f6;
}

.stepper {
    display: flex;
    align-items: center;
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
}

.stepper-btn {
    width: 26px;
    height: 26px;
    display: flex;
    align-items: center;
    justify-content: center;
    border: none;
    background: transparent;
    color: var(--text-secondary);
    font-size: 1rem;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.stepper-btn:hover {
    background: var(--bg-hover);
    color: var(--accent-cyan);
}

.stepper-btn:active {
    background: rgba(0, 245, 212, 0.2);
}

.stepper-value {
    min-width: 20px;
    font-family: var(--font-mono);
    font-size: 0.85rem;
    font-weight: 600;
    color: var(--text-primary);
    text-align: center;
}

/* === Supercell Button === */
.btn-supercell {
    width: 100%;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    padding: 0.65rem 1rem;
    background: linear-gradient(135deg, rgba(155, 93, 229, 0.15), rgba(241, 91, 181, 0.15));
    border: 1px solid rgba(155, 93, 229, 0.4);
    border-radius: var(--radius-sm);
    color: var(--accent-purple);
    font-size: 0.85rem;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.btn-supercell:hover:not(:disabled) {
    background: linear-gradient(135deg, rgba(155, 93, 229, 0.25), rgba(241, 91, 181, 0.25));
    border-color: var(--accent-purple);
    box-shadow: 0 0 12px rgba(155, 93, 229, 0.3);
}

.btn-supercell:disabled {
    opacity: 0.4;
    cursor: not-allowed;
}

.btn-supercell svg {
    opacity: 0.9;
}

/* === Vacuum Info === */
.vacuum-info {
    margin-top: 0.25rem;
}

.vacuum-hint {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-size: 0.75rem;
    color: var(--text-muted);
    padding: 0.5rem 0.75rem;
    background: rgba(254, 228, 64, 0.05);
    border-radius: var(--radius-sm);
    border: 1px dashed rgba(254, 228, 64, 0.2);
}

.vacuum-hint svg {
    color: var(--accent-yellow);
    flex-shrink: 0;
    opacity: 0.8;
}

/* === Edit Mode Controls === */
.edit-mode-only {
    animation: slideDown 0.2s ease;
}

@keyframes slideDown {
    from {
        opacity: 0;
        transform: translateY(-8px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* === Control Divider === */
.control-divider {
    height: 1px;
    background: linear-gradient(90deg, transparent, var(--border-color), transparent);
    margin: 1rem 0;
}

/* === Animations === */
@keyframes pulse {
    0%, 100% { opacity: 1; }
    50% { opacity: 0.5; }
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

.fade-in {
    animation: fadeIn 0.3s ease forwards;
}

/* === Responsive === */
@media (max-width: 768px) {
    .sidebar {
        width: var(--sidebar-width, 240px);
    }
    
    .viewport-guidance {
        display: none;
    }
}

/* === Selective Dynamics UI === */
.sel-status {
    margin-left: auto;
    font-size: 0.8rem;
}

.sel-status.partial {
    font-family: var(--font-mono);
    font-size: 0.7rem;
    letter-spacing: 0.05em;
    color: #ffaa00;
    white-space: nowrap;
}

/* Constraints of the selected atoms: one toggle per axis */
.constraint-controls {
    margin: 0.8rem 0;
    padding: 0.75rem;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    background: var(--bg-tertiary);
}

.constraint-controls .axis-toggle,
.constraint-controls .btn {
    background: var(--bg-secondary);
}

.constraint-label {
    font-size: 0.7rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-muted);
    margin-bottom: 0.4rem;
}

.constraint-axes {
    display: flex;
    gap: 0.4rem;
    margin-bottom: 0.25rem;
}

.constraint-controls .sd-buttons {
    margin-bottom: 0.5rem;
}

.axis-toggle {
    flex: 1;
    min-width: 0;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 0.1rem;
    padding: 0.35rem 0.25rem;
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    color: var(--text-secondary);
    font: inherit;
    cursor: pointer;
    transition: background 0.15s, border-color 0.15s, color 0.15s;
}

.axis-toggle .axis-name {
    font-family: var(--font-mono);
    font-size: 0.95rem;
    font-weight: 600;
    line-height: 1;
    color: var(--text-primary);
}

.axis-toggle .axis-state {
    font-size: 0.65rem;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    line-height: 1;
}

.axis-toggle:hover {
    border-color: var(--text-muted);
}

.axis-toggle[data-state="fixed"] {
    background: rgba(255, 107, 107, 0.15);
    border-color: rgba(255, 107, 107, 0.5);
    color: #ff6b6b;
}

.axis-toggle[data-state="fixed"] .axis-name {
    color: #ff6b6b;
}

.axis-toggle[data-state="mixed"] {
    background: rgba(255, 170, 0, 0.12);
    border-color: rgba(255, 170, 0, 0.5);
    color: #ffaa00;
}

.axis-toggle[data-state="mixed"] .axis-name {
    color: #ffaa00;
}

.axis-toggle:focus-visible {
    outline: 2px solid var(--accent-cyan);
    outline-offset: 1px;
}

.constraint-hint {
    font-size: 0.75rem;
    color: var(--text-muted);
    text-align: center;
    margin: 0.5rem 0 0.75rem;
}

/* === Select Atoms (by element or coordinate range) === */
/* === Select Atoms: one quiet pill idiom, a label column, header actions === */
.select-head {
    display: flex;
    flex-wrap: wrap;
    align-items: baseline;
    justify-content: space-between;
    gap: 0.25rem 0.5rem;
    margin-bottom: 0.75rem;
}

.select-head .sd-batch-title {
    margin-bottom: 0;
}

.select-set-actions {
    display: flex;
    align-items: baseline;
    gap: 0.35rem;
}

.text-action {
    padding: 0;
    background: none;
    border: none;
    color: var(--text-secondary);
    font: inherit;
    font-size: 0.75rem;
    cursor: pointer;
    transition: color 0.15s;
}

.text-action:hover {
    color: var(--accent-cyan);
}

.text-action[disabled] {
    color: var(--text-muted);
    opacity: 0.6;
    cursor: default;
}

.text-action:focus-visible {
    outline: 2px solid var(--accent-cyan);
    outline-offset: 2px;
    border-radius: 2px;
}

.text-action-sep {
    font-size: 0.75rem;
    color: var(--text-muted);
}

.select-row {
    display: flex;
    align-items: flex-start;
    gap: 0.5rem;
    margin-bottom: 0.6rem;
}

.select-label {
    flex: 0 0 55px;
    line-height: 30px;
    font-size: 0.85rem;
    color: var(--text-secondary);
}

.select-row-indent {
    padding-left: calc(55px + 0.5rem);
}

/* The pill: every small control in the section shares this shape and height */
.pill {
    display: inline-flex;
    align-items: center;
    gap: 0.35rem;
    height: 30px;
    padding: 0 0.7rem;
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: 999px;
    color: var(--text-primary);
    font: inherit;
    font-size: 0.8rem;
    line-height: 1;
    cursor: pointer;
    transition: background 0.15s, border-color 0.15s, color 0.15s;
}

.pill:hover {
    border-color: var(--text-muted);
}

.pill[aria-pressed="true"] {
    background: rgba(0, 245, 212, 0.15);
    border-color: var(--accent-cyan);
    color: var(--accent-cyan);
}

.pill:focus-visible {
    outline: 2px solid var(--accent-cyan);
    outline-offset: 1px;
}

.pill-static {
    cursor: default;
    color: var(--text-muted);
}

.pill-select {
    appearance: none;
    -webkit-appearance: none;
    padding-right: 1.6rem;
    font-family: var(--font-mono);
    background-image: linear-gradient(45deg, transparent 50%, var(--text-secondary) 50%), linear-gradient(135deg, var(--text-secondary) 50%, transparent 50%);
    background-position: calc(100% - 0.9rem) 55%, calc(100% - 0.6rem) 55%;
    background-size: 0.3rem 0.3rem, 0.3rem 0.3rem;
    background-repeat: no-repeat;
}

.pill-input {
    flex: 1 1 4rem;
    min-width: 4rem;
    width: auto;
    padding: 0 0.5rem;
    font-family: var(--font-mono);
    text-align: center;
    cursor: text;
}

.pill-input::placeholder {
    color: var(--text-muted);
}

.pill-input:focus {
    outline: none;
    border-color: var(--accent-cyan);
    box-shadow: 0 0 0 2px rgba(0, 245, 212, 0.15);
}

.element-chips {
    display: flex;
    flex-wrap: wrap;
    gap: 0.35rem;
}

.element-chip {
    padding: 0 0.6rem 0 0.5rem;
}

.chip-dot {
    width: 0.5rem;
    height: 0.5rem;
    border-radius: 50%;
    background: var(--chip-color, var(--text-muted));
    flex: none;
}

.chip-element {
    font-weight: 600;
}

.chip-count {
    font-family: var(--font-mono);
    font-size: 0.7rem;
    color: var(--text-muted);
}

.element-chip[data-state="some"] {
    border-color: rgba(0, 245, 212, 0.45);
}

.element-chip[aria-pressed="true"] .chip-count {
    color: var(--accent-cyan);
}

.select-range-row {
    display: flex;
    align-items: center;
    gap: 0.4rem;
    width: 100%;
}

.select-range-to {
    font-size: 0.8rem;
    color: var(--text-muted);
}

/* Cartesian / fractional as a pill pair over ordinary radios */
.choice-pills {
    display: inline-flex;
}

.choice-pills .pill {
    position: relative;
    border-radius: 0;
    padding: 0 0.6rem;
    cursor: pointer;
}

.choice-pills .pill:first-child {
    border-radius: 999px 0 0 999px;
}

.choice-pills .pill:last-child {
    border-radius: 0 999px 999px 0;
}

.choice-pills .pill + .pill {
    margin-left: -1px;
}

.choice-pills input[type="radio"] {
    position: absolute;
    inset: 0;
    width: 100%;
    height: 100%;
    margin: 0;
    opacity: 0;
    cursor: pointer;
}

.choice-pills .pill:has(input:checked) {
    background: rgba(0, 245, 212, 0.15);
    border-color: var(--accent-cyan);
    color: var(--accent-cyan);
    z-index: 1;
}

.choice-pills .pill:has(input:focus-visible) {
    outline: 2px solid var(--accent-cyan);
    outline-offset: 1px;
}

/* Move block header: label left, coordinate choice right */
.move-head {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 0.5rem;
    flex-wrap: wrap;
    margin-bottom: 0.6rem;
}

.move-head .constraint-label,
.move-head .sd-batch-title {
    margin-bottom: 0;
}

/* Stays on the right even when a narrow panel wraps it to its own line */
.move-head .choice-pills {
    margin-left: auto;
}

.add-atom-head {
    margin-bottom: 0.75rem;
}

/* No unit cell, no choice: the same pill shape, read-only. Grey outline,
   muted text, no fill, cyan or hover, so it lines up with the switchable
   pair without offering to switch. */
.choice-pills.single .pill,
.choice-pills.single .pill:hover,
.choice-pills.single .pill:has(input:checked) {
    background: none;
    border-color: var(--border-color);
    border-radius: 999px;
    color: var(--text-muted);
    cursor: default;
}

.choice-pills.single input[type="radio"] {
    cursor: default;
}

/* Select Atoms is the first section: no rule above it */
.sd-batch-section.select-rule-section {
    margin-top: 0.25rem;
    padding-top: 0;
    border-top: none;
}

/* Structure: whole-structure actions, with the constraint summary in the head */
.structure-section .sd-stats {
    padding: 0;
    background: none;
    font-size: 0.75rem;
}

.structure-actions {
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
}

.structure-actions .btn {
    flex: 1 1 auto;
}

.select-range-btn {
    width: 100%;
}

.btn-select {
    background: rgba(0, 245, 212, 0.15);
    border: 1px solid rgba(0, 245, 212, 0.4);
    color: var(--accent-cyan);
}

.btn-select:hover {
    background: rgba(0, 245, 212, 0.25);
    border-color: var(--accent-cyan);
}

/* Box select: the rectangle drawn over the canvas and its panel button */
#boxSelectRect {
    position: absolute;
    z-index: 5;
    pointer-events: none;
    border: 1px dashed var(--accent-cyan);
    background: rgba(0, 245, 212, 0.08);
    border-radius: 2px;
}

#boxSelectRect.remove {
    border-color: #ff6b6b;
    background: rgba(255, 107, 107, 0.08);
}

#boxSelectRect[hidden] {
    display: none;
}

/* Box gestures only apply in Edit mode */
.controls-hint .edit-hint {
    display: none;
}

body.edit-mode-active .controls-hint .edit-hint {
    display: inline;
}

.sd-batch-buttons .btn {
    flex: 1;
}

.select-range-to {
    font-size: 0.8rem;
    color: var(--text-muted);
}

.btn-select {
    background: rgba(0, 245, 212, 0.15);
    border: 1px solid rgba(0, 245, 212, 0.4);
    color: var(--accent-cyan);
}

.btn-select:hover {
    background: rgba(0, 245, 212, 0.25);
    border-color: var(--accent-cyan);
}

/* Error lines take no room until there is something to say */
.add-atom-error:empty {
    min-height: 0;
    margin: 0;
}


.sd-buttons {
    display: flex;
    gap: 0.5rem;
    margin-bottom: 0.75rem;
}

.sd-buttons .btn {
    flex: 1;
    padding: 0.5rem 0.75rem;
    font-size: 0.8rem;
}

.btn-fix,
.btn-unfix {
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    color: var(--text-primary);
}

.btn-fix:hover,
.btn-unfix:hover {
    border-color: var(--text-muted);
}

.sd-batch-section {
    margin-top: 1rem;
    padding-top: 1rem;
    border-top: 1px solid var(--border-color);
}

.sd-batch-title {
    font-size: 0.75rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-secondary);
    margin-bottom: 0.75rem;
}

.z-threshold-input {
    width: 100%;
    min-width: 0;
    padding: 0.35rem 0.5rem;
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    color: var(--text-primary);
    font-family: var(--font-mono);
    font-size: 0.85rem;
    text-align: center;
}

.z-threshold-input:focus {
    outline: none;
    border-color: var(--accent-cyan);
    box-shadow: 0 0 0 2px rgba(0, 245, 212, 0.15);
}

.sd-batch-buttons {
    display: flex;
    gap: 0.5rem;
    margin-bottom: 0.75rem;
}

.btn-sm {
    padding: 0.4rem 0.75rem;
    font-size: 0.75rem;
}

.sd-stats {
    font-size: 0.8rem;
    color: var(--text-muted);
    text-align: center;
    padding: 0.5rem;
    background: var(--bg-tertiary);
    border-radius: var(--radius-sm);
}

/* Fixed atom badges in atom list */
.fixed-badge {
    font-size: 0.7rem;
    margin-left: 0.25rem;
    opacity: 0.8;
}

.sd-info {
    font-size: 0.85rem;
}

/* Info value for selective dynamics */
.info-value.sd-info {
    color: var(--text-secondary);
}

/* === Add Atom Section === */
.add-atom-section {
    margin-top: 1rem;
    padding-top: 1rem;
    border-top: 1px solid var(--border-color);
}

.add-atom-row {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    margin-bottom: 0.75rem;
}

.add-atom-row label {
    font-size: 0.85rem;
    color: var(--text-secondary);
    min-width: 55px;
}

.element-select {
    flex: 1;
    padding: 0.4rem 0.5rem;
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    color: var(--text-primary);
    font-family: var(--font-mono);
    font-size: 0.85rem;
    cursor: pointer;
}

.element-select:focus {
    outline: none;
    border-color: var(--accent-cyan);
    box-shadow: 0 0 0 2px rgba(0, 245, 212, 0.15);
}

.add-atom-coord-type {
    display: flex;
    gap: 1rem;
    margin-bottom: 0.75rem;
}

.coord-type-label {
    display: flex;
    align-items: center;
    gap: 0.35rem;
    font-size: 0.8rem;
    color: var(--text-secondary);
    cursor: pointer;
}

.coord-type-label input[type="radio"] {
    accent-color: var(--accent-cyan);
}

.add-atom-coords {
    display: flex;
    gap: 0.5rem;
    margin: 0.6rem 0;
}

.coord-input-group {
    flex: 1;
    display: flex;
    flex-direction: column;
    gap: 0.25rem;
}

.coord-input-group label {
    font-size: 0.75rem;
    color: var(--text-muted);
    text-align: center;
    font-family: var(--font-mono);
}

.coord-input {
    width: 100%;
    height: 30px;
    padding: 0 0.5rem;
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: 999px;
    color: var(--text-primary);
    font-family: var(--font-mono);
    font-size: 0.8rem;
    text-align: center;
}

.coord-input:focus {
    outline: none;
    border-color: var(--accent-cyan);
    box-shadow: 0 0 0 2px rgba(0, 245, 212, 0.15);
}

.add-atom-error {
    font-size: 0.8rem;
    color: #ff6b6b;
    min-height: 1.2rem;
    margin-bottom: 0.5rem;
    text-align: center;
}

.add-atom-error.success {
    color: var(--accent-cyan);
}

.btn-add-atom {
    width: 100%;
    padding: 0.5rem 1rem;
    background: rgba(0, 245, 212, 0.15);
    border: 1px solid rgba(0, 245, 212, 0.4);
    color: var(--accent-cyan);
    font-weight: 500;
}

.btn-add-atom:hover {
    background: rgba(0, 245, 212, 0.25);
    border-color: var(--accent-cyan);
}

/* === Global Periodic Shift === */
.shift-hint {
    font-size: 0.75rem;
    color: var(--text-muted);
    margin-bottom: 0.5rem;
}

.shift-target-hint {
    font-size: 0.75rem;
    color: var(--accent-cyan);
    margin-bottom: 0.5rem;
    padding: 0.25rem 0.5rem;
    background: rgba(0, 245, 212, 0.1);
    border-radius: var(--radius-sm);
    text-align: center;
}

.shift-coords {
    display: flex;
    gap: 0.5rem;
    margin-bottom: 0.6rem;
}

.shift-input-group {
    flex: 1;
    display: flex;
    flex-direction: column;
    gap: 0.25rem;
}

.shift-input-group label {
    font-size: 0.75rem;
    color: var(--text-muted);
    text-align: center;
    font-family: var(--font-mono);
}

.shift-input {
    width: 100%;
    height: 30px;
    padding: 0 0.5rem;
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: 999px;
    color: var(--text-primary);
    font-family: var(--font-mono);
    font-size: 0.8rem;
    text-align: center;
}

.shift-input:focus {
    outline: none;
    border-color: var(--accent-cyan);
    box-shadow: 0 0 0 2px rgba(0, 245, 212, 0.15);
}

.btn-shift {
    width: 100%;
    padding: 0.5rem 1rem;
    background: rgba(0, 245, 212, 0.15);
    border: 1px solid rgba(0, 245, 212, 0.4);
    color: var(--accent-cyan);
    font-weight: 500;
}

.btn-shift:hover {
    background: rgba(0, 245, 212, 0.25);
    border-color: var(--accent-cyan);
}

.shift-quick-buttons {
    display: flex;
    gap: 0.5rem;
}

.btn-quick {
    flex: 1;
    background: rgba(254, 228, 64, 0.1);
    border: 1px solid rgba(254, 228, 64, 0.3);
    color: var(--accent-yellow);
}

.btn-quick:hover {
    background: rgba(254, 228, 64, 0.2);
    border-color: var(--accent-yellow);
}

/* === Timeline Panel (XDATCAR) === */
.timeline-panel {
    background: var(--bg-secondary);
    border-top: 1px solid var(--border-color);
    padding: 0.5rem 1rem;
    display: flex;
    align-items: center;
    justify-content: center;
}

.timeline-panel.hidden {
    display: none;
}

.timeline-controls {
    display: flex;
    align-items: center;
    gap: 1rem;
    width: 100%;
    max-width: 900px;
}

/* Play/Pause button */
.timeline-btn {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 40px;
    height: 40px;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    background: var(--bg-tertiary);
    color: var(--text-secondary);
    cursor: pointer;
    transition: all var(--transition-fast);
    flex-shrink: 0;
}

.timeline-btn:hover {
    background: var(--bg-hover);
    color: var(--text-primary);
    border-color: var(--accent-purple);
}

.timeline-btn:active {
    background: rgba(155, 93, 229, 0.2);
}

.timeline-btn.play-btn {
    background: linear-gradient(135deg, rgba(155, 93, 229, 0.2), rgba(241, 91, 181, 0.2));
    border-color: var(--accent-purple);
    color: var(--accent-purple);
}

.timeline-btn.play-btn:hover {
    background: linear-gradient(135deg, rgba(155, 93, 229, 0.3), rgba(241, 91, 181, 0.3));
    box-shadow: 0 0 12px rgba(155, 93, 229, 0.3);
}

.timeline-btn.play-btn.playing {
    background: linear-gradient(135deg, rgba(241, 91, 181, 0.3), rgba(255, 107, 107, 0.2));
    border-color: var(--accent-pink);
    color: var(--accent-pink);
}

/* Show/hide play/pause icons based on state */
.timeline-btn.play-btn .pause-icon {
    display: none;
}

.timeline-btn.play-btn.playing .play-icon {
    display: none;
}

.timeline-btn.play-btn.playing .pause-icon {
    display: block;
}

/* Timeline slider */
.timeline-slider-container {
    flex: 1;
    display: flex;
    align-items: center;
    min-width: 150px;
}

.timeline-slider {
    width: 100%;
    height: 8px;
    border-radius: 4px;
    background: var(--bg-tertiary);
    appearance: none;
    cursor: pointer;
    border: 1px solid var(--border-color);
}

.timeline-slider::-webkit-slider-thumb {
    appearance: none;
    width: 18px;
    height: 18px;
    border-radius: 50%;
    background: linear-gradient(135deg, var(--accent-purple), var(--accent-pink));
    cursor: pointer;
    box-shadow: 0 0 8px rgba(155, 93, 229, 0.5);
    transition: transform var(--transition-fast);
}

.timeline-slider::-webkit-slider-thumb:hover {
    transform: scale(1.15);
}

.timeline-slider::-webkit-slider-runnable-track {
    height: 6px;
    border-radius: 3px;
}

/* Frame info section */
.timeline-info {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    flex-shrink: 0;
}

.frame-display {
    font-family: var(--font-mono);
    font-size: 0.85rem;
    font-weight: 600;
    color: var(--accent-purple);
    min-width: 70px;
    text-align: center;
}

.timeline-separator {
    width: 1px;
    height: 20px;
    background: var(--border-color);
}

/* Loop toggle */
.loop-toggle {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 32px;
    height: 32px;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    background: var(--bg-tertiary);
    color: var(--text-muted);
    cursor: pointer;
    transition: all var(--transition-fast);
}

.loop-toggle:hover {
    background: var(--bg-hover);
    color: var(--text-secondary);
}

.loop-toggle input {
    display: none;
}

.loop-toggle input:checked + svg {
    color: var(--accent-cyan);
}

.loop-toggle:has(input:checked) {
    border-color: var(--accent-cyan);
    background: rgba(0, 245, 212, 0.1);
}

/* FPS control */
.fps-control {
    display: flex;
    align-items: center;
    gap: 0.35rem;
}

.fps-control label {
    font-size: 0.75rem;
    color: var(--text-muted);
}

.fps-select {
    padding: 0.25rem 0.5rem;
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    color: var(--text-primary);
    font-family: var(--font-mono);
    font-size: 0.8rem;
    cursor: pointer;
}

.fps-select:focus {
    outline: none;
    border-color: var(--accent-purple);
}

/* Edit mode disabled indicator for XDATCAR */
.mode-btn[data-mode="edit"]:disabled {
    opacity: 0.4;
    cursor: not-allowed;
    pointer-events: none;
}

/* XDATCAR file type badge in Structure Info */
.file-type-badge {
    display: inline-block;
    padding: 0.15rem 0.5rem;
    border-radius: 10px;
    font-size: 0.7rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.file-type-badge.poscar {
    background: rgba(0, 245, 212, 0.2);
    color: var(--accent-cyan);
}

.file-type-badge.xdatcar {
    background: rgba(155, 93, 229, 0.2);
    color: var(--accent-purple);
}

.file-type-badge.xyz {
    background: rgba(254, 228, 64, 0.2);
    color: #fee440;
}

.file-type-badge.cif {
    background: rgba(241, 91, 181, 0.2);
    color: var(--accent-pink);
}

/* Responsive timeline */
@media (max-width: 768px) {
    .timeline-controls {
        flex-wrap: wrap;
        gap: 0.5rem;
    }
    
    .timeline-slider-container {
        order: 3;
        width: 100%;
        min-width: auto;
    }
    
    .fps-control {
        display: none;
    }
}

/* The divider stays reachable when the panel is collapsed. */
.sidebar[aria-hidden="true"] { visibility: hidden; border: 0; }
.sidebar-divider {
    flex: 0 0 10px;
    cursor: col-resize;
    touch-action: none;
    background: var(--bg-secondary);
    position: relative;
}
.sidebar-divider::after {
    content: '';
    position: absolute;
    width: 3px;
    height: 42px;
    top: calc(50% - 21px);
    left: 3px;
    border-radius: 3px;
    background: var(--text-muted);
}
.sidebar-divider:hover::after,
.sidebar-divider:focus-visible::after,
.resizing-sidebar .sidebar-divider::after { background: var(--accent-cyan); }
.sidebar-divider:focus-visible { outline: 1px solid var(--accent-cyan); outline-offset: -1px; }
.resizing-sidebar { user-select: none; cursor: col-resize; }

@media (max-width: 1100px) {
    .header { flex-wrap: wrap; gap: .6rem; padding: .6rem 1rem; }
    .logo-text { white-space: nowrap; }
    .header-controls { width: 100%; flex-wrap: wrap; }
    .header-controls > * { flex-shrink: 0; }
}

/* Reflow according to the user-selected panel width, not just screen width. */
@container sidebar (max-width: 260px) {
    .panel { padding: .85rem .75rem; }
    .info-item { flex-direction: column; gap: .2rem; }
    .info-label { margin-right: 0; }
    .info-value { text-align: left; }
    .periodic-row, .add-atom-coord-type, .add-atom-coords, .shift-coords,
    .sd-buttons, .sd-batch-buttons, .select-row { flex-wrap: wrap; }
    .select-row-indent { padding-left: 0; }
    .periodic-axis { flex: 1 1 74px; min-width: 74px; }
    .coord-input-group, .shift-input-group { flex: 1 1 60px; min-width: 0; }
    .element-select { min-width: 0; }
    .meas-content { min-width: 0; flex-wrap: wrap; gap: .3rem; }
    .meas-delta { flex-wrap: wrap; }
    .delta-item { flex: 1 1 70px; }
    .sel-coords { padding-left: 0; overflow-wrap: anywhere; }
}

/* === Display panel: background swatches and Reset all === */
.appearance-actions {
    display: block; /* its own subsection: label, button, note, all on the panel's left edge */
}

/* A plain button, dimmed while nothing differs from the defaults; the pink
   appears only on hover, so the button informs without inviting. */
.btn-reset {
    display: inline-flex;
    gap: 0.45rem;
    font-size: 0.85rem;
    padding: 0.45rem 0.85rem;
}

.btn-reset:not(:disabled):hover {
    border-color: var(--accent-pink);
    color: var(--accent-pink);
}

.appearance-note {
    margin: 0.75rem 0 0;
    font-size: 0.75rem;
    color: var(--text-muted);
}

.control-label {
    display: block;
    font-size: 0.8rem;
    color: var(--text-secondary);
    margin-bottom: 0.5rem;
}

.swatch-row {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 0.6rem;
}

.swatch {
    width: 26px;
    height: 26px;
    padding: 0;
    border-radius: 50%;
    border: 1px solid var(--border-color);
    background: var(--swatch);
    cursor: pointer;
    transition: transform var(--transition-fast), box-shadow var(--transition-fast);
}

.swatch:hover {
    transform: scale(1.12);
}

.swatch.selected {
    box-shadow: 0 0 0 2px var(--bg-secondary), 0 0 0 4px var(--accent-cyan);
}

.control-group .swatch-custom {
    position: relative;
    display: block;
    margin: 0;
    overflow: hidden;
    border-style: dashed;
    background: var(--swatch, conic-gradient(#f15bb5, #fee440, #00f5d4, #9b5de5, #f15bb5));
}

.swatch-custom input {
    position: absolute;
    inset: -4px;
    width: calc(100% + 8px);
    height: calc(100% + 8px);
    opacity: 0;
    cursor: pointer;
}

/* === Element colour pickers in the Atoms panel === */
.atom-sphere {
    position: relative;
    flex-shrink: 0;
    overflow: hidden;
    cursor: pointer;
    transition: transform var(--transition-fast);
}

.atom-sphere:hover {
    transform: scale(1.1);
}

.atom-sphere:focus-within {
    outline: 2px solid var(--accent-cyan);
    outline-offset: 2px;
}

.atom-color-input {
    position: absolute;
    inset: -4px;
    width: calc(100% + 8px);
    height: calc(100% + 8px);
    opacity: 0;
    cursor: pointer;
}

.atom-color-reset {
    display: none;
    margin-left: auto;
    padding: 0.15rem 0.45rem;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    background: transparent;
    color: var(--text-muted);
    font-size: 0.7rem;
    cursor: pointer;
}

.atom-entry.recoloured .atom-color-reset {
    display: inline-block;
}

.atom-color-reset:hover {
    color: var(--accent-cyan);
    border-color: var(--accent-cyan);
}

/* The button and the question take turns; their display rules would otherwise beat the hidden attribute. */
.btn-reset[hidden],
.reset-confirm[hidden] {
    display: none;
}

.reset-confirm {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    min-height: 2.2rem;
}

.reset-confirm-text {
    font-size: 0.85rem;
    color: var(--text-primary);
}

.btn-reset-yes,
.btn-reset-no {
    font-size: 0.8rem;
    padding: 0.35rem 0.7rem;
}

.btn-reset-yes {
    border-color: var(--accent-pink);
    color: var(--accent-pink);
}

.btn-reset-yes:hover {
    background: rgba(241, 91, 181, 0.15);
    color: var(--text-primary);
}

/* === Export menu === */
.export-wrap {
    position: relative;
}

.export-menu {
    position: absolute;
    right: 0;
    top: calc(100% + 6px);
    min-width: 250px;
    padding: 0.4rem;
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: 10px;
    box-shadow: 0 12px 32px rgba(0, 0, 0, 0.45);
    z-index: 50;
}

.export-menu[hidden],
.export-section[hidden],
.export-divider[hidden] {
    display: none;
}

.export-item {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 1rem;
    width: 100%;
    padding: 0.55rem 0.7rem;
    border: 0;
    border-radius: var(--radius-sm);
    background: transparent;
    color: var(--text-primary);
    font: inherit;
    font-size: 0.875rem;
    text-align: left;
    cursor: pointer;
}

.export-item:hover {
    background: var(--bg-hover);
}

.export-item-title {
    font-weight: 500;
}

.export-item-meta {
    font-family: var(--font-mono);
    font-size: 0.7rem;
    color: var(--text-muted);
}

.export-divider {
    height: 1px;
    margin: 0.3rem 0.4rem;
    background: var(--border-color);
}

.export-section {
    display: grid;
    gap: 0.5rem;
    padding: 0.45rem 0.7rem 0.6rem;
    font-size: 0.875rem;
}

.export-row {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 0.75rem;
    font-size: 0.8rem;
    color: var(--text-secondary);
}

.export-sizes {
    display: inline-flex;
    overflow: hidden;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
}

.export-size {
    padding: 0.25rem 0.6rem;
    border: 0;
    background: transparent;
    color: var(--text-secondary);
    font: inherit;
    font-size: 0.8rem;
    cursor: pointer;
}

.export-size + .export-size {
    border-left: 1px solid var(--border-color);
}

.export-size.active {
    background: rgba(0, 245, 212, 0.15);
    color: var(--accent-cyan);
}

.export-pixels {
    margin-top: -0.25rem;
    font-family: var(--font-mono);
    font-size: 0.7rem;
    color: var(--text-muted);
    text-align: right;
}

.export-check {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-size: 0.8rem;
    color: var(--text-secondary);
    cursor: pointer;
}

.export-save {
    justify-content: center;
    padding: 0.4rem 0.75rem;
    font-size: 0.8rem;
}

.export-hint {
    margin-top: -0.2rem;
    font-size: 0.72rem;
    line-height: 1.4;
    color: var(--text-muted);
}