:root {
    /* Colors */
    --bg-color: #f0f2f5;
    --text-primary: #1f2937;
    --text-secondary: #6b7280;
    --accent-color: #3b82f6;
    --accent-hover: #2563eb;
    --panel-bg: rgba(255, 255, 255, 0.95);
    --border-color: #e5e7eb;
    --input-bg: #f9fafb;
    --shadow-sm: 0 1px 2px 0 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);

    /* Spacing */
    --space-xs: 4px;
    --space-sm: 8px;
    --space-md: 16px;
    --space-lg: 24px;

    /* Radius */
    --radius-sm: 4px;
    --radius-md: 8px;
    --radius-lg: 12px;
}

body {
    margin: 0;
    display: flex;
    height: 100vh;
    font-family: 'Inter', system-ui, -apple-system, sans-serif;
    color: var(--text-primary);
    background-color: var(--bg-color);
    overflow: hidden;
    /* Prevent body scroll because sidebar/viewer handle it */
}

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

::-webkit-scrollbar-track {
    background: transparent;
}

::-webkit-scrollbar-thumb {
    background: #cbd5e1;
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: #94a3b8;
}

/* Header */
.app-header {
    margin-bottom: var(--space-lg);
    padding-bottom: var(--space-md);
    border-bottom: 1px solid var(--border-color);
}

.app-header h2 {
    margin: 0 0 var(--space-xs) 0;
    font-size: 1.125rem;
    font-weight: 700;
    line-height: 1.4;
    color: var(--text-primary);
    letter-spacing: -0.01em;
}

.app-header .subtitle {
    font-size: 0.875rem;
    color: var(--text-secondary);
    font-weight: 500;
}

/* Sidebar / UI Panel */
#ui {
    width: 340px;
    padding: var(--space-lg);
    box-sizing: border-box;
    background: var(--panel-bg);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    overflow-y: auto;
    border-right: 1px solid var(--border-color);
    flex-shrink: 0;
    box-shadow: var(--shadow-sm);
    z-index: 10;
    display: flex;
    flex-direction: column;
    gap: var(--space-md);
}

#viewer {
    flex: 1;
    background-color: #333;
    /* Fallback/Loading bg */
    position: relative;
}

/* Typography */
h3 {
    font-size: 0.85rem;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-secondary);
    margin: var(--space-md) 0 var(--space-sm) 0;
    font-weight: 600;
}

/* Feature List (Details/Summary) */
.feature-root {
    margin-top: var(--space-md);
}

.feature-root details {
    background: var(--input-bg);
    border-radius: var(--radius-md);
    border: 1px solid var(--border-color);
    transition: all 0.2s ease;
}

.feature-root summary {
    padding: var(--space-sm) var(--space-md);
    cursor: pointer;
    list-style: none;
    display: flex;
    align-items: center;
    justify-content: space-between;
    font-size: 0.85rem;
    font-weight: 500;
    color: var(--text-primary);
    user-select: none;
}

.feature-root summary::-webkit-details-marker {
    display: none;
}

.feature-root summary::after {
    content: '+';
    font-size: 1.25rem;
    font-weight: 300;
    color: var(--text-secondary);
    transition: transform 0.2s;
}

.feature-root details[open] summary::after {
    transform: rotate(45deg);
}

.feature-list-content {
    padding: 0 var(--space-md) var(--space-md);
    color: var(--text-secondary);
    font-size: 0.8rem;
    line-height: 1.5;
    border-top: 1px solid var(--border-color);
}

.feature-item {
    margin-top: var(--space-sm);
}

.f-title {
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 2px;
}

/* Forms & Inputs */
fieldset {
    border: 1px solid var(--border-color);
    padding: var(--space-md);
    margin: 0;
    border-radius: var(--radius-md);
    background: white;
    margin-bottom: var(--space-md);
}

legend {
    font-size: 0.75rem;
    font-weight: 600;
    color: var(--accent-color);
    padding: 0 var(--space-xs);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

label {
    display: block;
    font-size: 0.8rem;
    font-weight: 500;
    color: var(--text-secondary);
    margin-bottom: var(--space-xs);
}

input[type="number"],
select {
    width: 100%;
    padding: 8px 12px;
    font-size: 0.9rem;
    font-family: inherit;
    color: var(--text-primary);
    background-color: var(--input-bg);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    transition: border-color 0.2s, box-shadow 0.2s;
    box-sizing: border-box;
}

input[type="number"]:focus,
select:focus {
    outline: none;
    border-color: var(--accent-color);
    box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
    background: white;
}

.row {
    display: flex;
    gap: var(--space-sm);
    margin-top: var(--space-sm);
}

.row>div {
    flex: 1;
}

.small {
    font-size: 0.75rem;
    color: var(--text-secondary);
    line-height: 1.4;
    margin-top: var(--space-xs);
}

hr {
    border: none;
    border-top: 1px dashed var(--border-color);
    margin: var(--space-md) 0;
}

/* Custom Checkbox Toggle */
.toggle-wrapper {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: var(--space-sm);
    cursor: pointer;
}

.toggle-wrapper input[type="checkbox"] {
    appearance: none;
    -webkit-appearance: none;
    width: 36px;
    height: 20px;
    background: #d1d5db;
    border-radius: 20px;
    position: relative;
    cursor: pointer;
    transition: background 0.3s;
    flex-shrink: 0;
}

.toggle-wrapper input[type="checkbox"]::after {
    content: '';
    position: absolute;
    top: 2px;
    left: 2px;
    width: 16px;
    height: 16px;
    background: white;
    border-radius: 50%;
    transition: transform 0.3s;
    box-shadow: 0 1px 2px rgba(0, 0, 0, 0.2);
}

.toggle-wrapper input[type="checkbox"]:checked {
    background: var(--accent-color);
}

.toggle-wrapper input[type="checkbox"]:checked::after {
    transform: translateX(16px);
}

.toggle-label {
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--text-primary);
}

/* Results Section */
#status {
    padding: var(--space-sm);
    background: #eff6ff;
    border-radius: var(--radius-sm);
    color: #1e40af;
    font-weight: 600;
    text-align: center;
    margin-bottom: var(--space-sm);
}

.highlight {
    font-weight: 600;
    color: var(--text-primary);
}

/* Measure Label */
#measureLabel {
    position: absolute;
    background: rgba(31, 41, 55, 0.9);
    color: white;
    padding: 4px 8px;
    font-size: 0.75rem;
    border-radius: 4px;
    pointer-events: none;
    display: none;
    z-index: 100;
    white-space: nowrap;
    box-shadow: var(--shadow-md);
    transform: translate(-50%, -100%);
    margin-top: -10px;
}

/* Menu Toggle Button (Mobile) */
#menuToggle {
    display: none;
    /* Hidden by default on desktop */
}

/* Responsive */
@media (max-width: 768px) {
    #menuToggle {
        display: flex;
        align-items: center;
        justify-content: center;
        position: absolute;
        top: 16px;
        left: 16px;
        z-index: 1001;
        width: 40px;
        height: 40px;
        background: white;
        border: none;
        border-radius: 50%;
        font-size: 1.25rem;
        cursor: pointer;
        box-shadow: var(--shadow-lg);
        color: var(--text-primary);
        padding: 0;
    }

    #ui {
        position: absolute;
        top: 0;
        left: 0;
        height: 100%;
        transform: translateX(-100%);
        /* Hidden */
        transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1);
        width: 85%;
        max-width: 320px;
    }

    #ui.menu-active {
        transform: translateX(0);
        /* Shown */
    }
}