:root {
    --primary-color: #ea8400;
    --primary-hover: #d67300;
    --primary-light: rgba(234, 132, 0, 0.1);
    --success-color: #10b981;
    --success-hover: #059669;
    --warning-color: #f59e0b;
    --danger-color: #ef4444;
    --surface-color: #ffffff;
    --surface-elevated: #f8fafc;
    --border-color: #e2e8f0;
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --text-muted: #94a3b8;
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
    --radius-sm: 6px;
    --radius-md: 10px;
    --radius-lg: 16px;
    --radius-xl: 24px;
    --transition-fast: 150ms ease;
    --transition-normal: 250ms ease;
    --transition-slow: 350ms ease;
}

.dark-mode {
    --primary-color: #ff9d1a;
    --primary-hover: #ea8400;
    --primary-light: rgba(255, 157, 26, 0.15);
    --surface-color: #1e293b;
    --surface-elevated: #334155;
    --border-color: #475569;
    --text-primary: #f1f5f9;
    --text-secondary: #cbd5e1;
    --text-muted: #94a3b8;
}

.tool-main {
    max-width: 1400px;
    margin: 0 auto;
    padding: 0 20px 40px;
}

.tool-header {
    text-align: center;
    padding: 36px 20px 24px;
}

.header-content {
    max-width: 820px;
    margin: 0 auto;
}

.icon-wave {
    font-size: 2.6rem;
}

/* the sidebar is long: let it scroll inside the viewport instead of hiding its end */
@media (min-width: 1025px) {
    body.tool-optics-lab .options-sidebar {
        max-height: calc(100vh - 40px);
        overflow-y: auto;
    }
}

.preset-note,
.control-note,
.boundary-note {
    margin: 10px 0 0;
    font-size: .82rem;
    line-height: 1.45;
    color: var(--optics-ink-2, var(--text-secondary));
}

.control-note a {
    font-weight: 600;
}

.passive-note .optics-badge {
    margin-right: 4px;
}

.preset-option.active {
    border-color: var(--primary-color);
    color: var(--text-primary);
}

.roc-row {
    display: flex;
    align-items: center;
    gap: 10px;
    margin-top: 4px;
}

.roc-row input.optics-num-input {
    width: 9em;
}

.roc-flat {
    display: inline-flex;
    align-items: center;
    gap: 6px;
    font-size: .85rem;
    color: var(--text-secondary);
}

.control-group .control-label sub {
    font-size: .7em;
}

.radio-group {
    border: 0;
    padding: 0;
    margin: 12px 0 0;
    display: flex;
    flex-wrap: wrap;
    gap: 6px 14px;
    font-size: .85rem;
    color: var(--text-secondary);
}

.radio-group legend {
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 6px;
    padding: 0;
}

.radio-group label {
    display: inline-flex;
    align-items: center;
    gap: 5px;
}

#orderSelect {
    width: 100%;
    min-height: 34px;
    margin-top: 4px;
    padding: 4px 8px;
    border-radius: 6px;
    border: 1px solid var(--border-color);
    background: var(--surface-color);
    color: var(--text-primary);
    font: inherit;
}

.button-row {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
    margin-top: 10px;
}

.button-row .action-btn,
.action-btn.full {
    flex: 1 1 auto;
    padding: 8px 10px;
    font-size: .82rem;
}

.action-btn.full {
    width: 100%;
}

.action-bar.compact {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
    margin: 0;
    padding: 0;
    justify-content: flex-start;
}

.action-bar.compact .action-btn {
    padding: 6px 12px;
    font-size: .82rem;
}

#specCanvas,
#gCanvas {
    cursor: crosshair;
}

#gCanvas.dragging {
    cursor: grabbing;
}

.canvas-area>.optics-readouts {
    padding: 12px 14px;
    border-radius: 12px;
    background: var(--optics-card-bg);
    border: 1px solid var(--optics-card-border);
}

.optics-warning {
    margin: 0 0 10px;
}

.optics-related {
    margin-top: 18px;
    padding: 14px 16px;
    border-radius: 12px;
    background: var(--optics-card-bg);
    border: 1px solid var(--optics-card-border);
    text-align: left;
}

.optics-related h2 {
    font-size: 1.1rem;
    margin: 0 0 8px;
}

.optics-related ul {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(min(260px, 100%), 1fr));
    gap: 6px 18px;
    margin: 0;
    padding-left: 18px;
}

.optics-related li span {
    display: block;
    font-size: .82rem;
    color: var(--optics-ink-2, var(--text-secondary));
}

.optics-teaching .formula-box p {
    overflow-wrap: anywhere;
}

@media (max-width: 760px) {
    .tool-main {
        padding: 0 10px 30px;
    }

    .tool-header {
        padding: 24px 6px 16px;
    }
}