:root {
    --bg-color: #0d1117;
    --surface-color: #161b22;
    --primary-color: #58a6ff;
    --success-color: #3fb950;
    --warning-color: #d29922;
    --danger-color: #f85149;
    --text-color: #e6edf3;
    --text-muted: #8b949e;
    --border-color: #30363d;
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: 'Inter', sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
    overflow: hidden;
}

/* App Layout */
.app-container {
    display: flex;
    height: 100vh;
}

/* Sidebar */
.sidebar {
    width: 260px;
    background-color: var(--surface-color);
    border-right: 1px solid var(--border-color);
    display: flex;
    flex-direction: column;
    overflow-y: auto;
    transition: left 0.3s ease;
    z-index: 1000;
}

.mobile-menu-btn {
    display: none;
    position: fixed;
    bottom: 20px;
    right: 20px;
    background: var(--primary-color);
    color: #fff;
    border: none;
    border-radius: 50%;
    width: 50px;
    height: 50px;
    font-size: 1.5rem;
    cursor: pointer;
    z-index: 1001;
    box-shadow: 0 4px 10px rgba(0,0,0,0.5);
    align-items: center;
    justify-content: center;
}

.logo {
    padding: 24px 20px;
    border-bottom: 1px solid var(--border-color);
    color: var(--primary-color);
}

.nav-links {
    list-style: none;
    padding: 20px 0;
}

.nav-links li {
    padding: 12px 24px;
    cursor: pointer;
    transition: background-color 0.2s, color 0.2s;
    color: var(--text-muted);
    font-size: 0.95rem;
    font-weight: 600;
}

.nav-links li:hover {
    background-color: rgba(88, 166, 255, 0.1);
    color: var(--text-color);
}

.nav-links li.active {
    background-color: rgba(88, 166, 255, 0.15);
    color: var(--primary-color);
    border-left: 4px solid var(--primary-color);
}

/* Main Content Area */
.content-area {
    flex-grow: 1;
    overflow-y: auto;
    padding: 40px;
    scroll-behavior: smooth;
    position: relative;
}

/* Pages */
.page {
    display: none;
    animation: fadeIn 0.4s ease forwards;
}

.page.active {
    display: block;
}

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

.page-header {
    margin-bottom: 30px;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 20px;
}

.page-header h1 {
    font-size: 2.2rem;
    color: var(--primary-color);
    margin-bottom: 10px;
}

/* Cards & UI Elements */
.card {
    background-color: var(--surface-color);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    padding: 24px;
    margin-bottom: 24px;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
}

.card h3 {
    margin-bottom: 12px;
    color: var(--text-color);
}

/* Grid Layouts */
.theory-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 20px;
}

/* Timeline */
.timeline {
    display: flex;
    justify-content: space-between;
    position: relative;
    padding: 20px 0;
}

.timeline::before {
    content: '';
    position: absolute;
    top: 30px;
    left: 0;
    width: 100%;
    height: 4px;
    background-color: var(--border-color);
    z-index: 0;
}

.timeline-item {
    position: relative;
    z-index: 1;
    text-align: center;
    width: 120px;
}

.timeline-dot {
    width: 20px;
    height: 20px;
    background-color: var(--bg-color);
    border: 4px solid var(--primary-color);
    border-radius: 50%;
    margin: 0 auto 10px auto;
    transition: transform 0.3s, box-shadow 0.3s;
}

.timeline-item:hover .timeline-dot {
    transform: scale(1.3);
    box-shadow: 0 0 10px var(--primary-color);
}

.timeline-content {
    font-size: 0.85rem;
    color: var(--text-muted);
}

/* Applications Grid */
.applications-grid {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
}

.app-chip {
    background-color: rgba(88, 166, 255, 0.1);
    color: var(--primary-color);
    padding: 8px 16px;
    border-radius: 20px;
    font-size: 0.9rem;
    border: 1px solid var(--primary-color);
}

/* Coordinate Mapping Demo */
.demo-container {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 20px;
}

.world-space, .screen-space {
    width: 300px;
    height: 300px;
    background-color: #000;
    border: 2px dashed var(--text-muted);
    position: relative;
    border-radius: 4px;
    overflow: hidden;
}

.world-space span, .screen-space span {
    position: absolute;
    top: 10px;
    left: 10px;
    color: var(--text-muted);
    font-size: 0.8rem;
    pointer-events: none;
}

.draggable-window {
    width: 100px;
    height: 100px;
    border: 2px solid var(--primary-color);
    background-color: rgba(88, 166, 255, 0.2);
    position: absolute;
    top: 50px;
    left: 50px;
    cursor: move;
}

.world-object {
    position: absolute;
    top: 100px;
    left: 150px;
    color: var(--warning-color);
    font-size: 24px;
}

.viewport-object {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    color: var(--warning-color);
    font-size: 24px;
    transition: all 0.1s ease-out;
}

.arrow {
    font-size: 2rem;
    color: var(--text-muted);
}

.calculations {
    font-family: monospace;
    background-color: #000;
    padding: 10px;
    border-radius: 4px;
    color: var(--success-color);
}

/* Button Component */
.btn {
    background-color: var(--surface-color);
    color: var(--text-color);
    border: 1px solid var(--border-color);
    padding: 8px 16px;
    border-radius: 4px;
    cursor: pointer;
    font-weight: 600;
    transition: all 0.2s;
}

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

.btn-primary {
    background-color: var(--primary-color);
    color: #fff;
    border: none;
}

.btn-primary:hover {
    background-color: #3b8ce8;
}

.btn-group {
    display: flex;
    gap: 10px;
    margin-bottom: 15px;
}

/* 3D Scene for Texture Mapping */
.scene3d {
    transform-style: preserve-3d;
}

@keyframes rotate3d {
    from { transform: rotateX(0deg) rotateY(0deg); }
    to { transform: rotateX(360deg) rotateY(360deg); }
}

@keyframes rotateBg {
    from { background-position: 0 0; }
    to { background-position: 200px 0; }
}

.cube-face {
    position: absolute;
    width: 100px;
    height: 100px;
    top: 50px;
    left: 50px;
    border: 1px solid var(--border-color);
}

.cube-face.front  { transform: translateZ(50px); }
.cube-face.back   { transform: rotateY(180deg) translateZ(50px); }
.cube-face.right  { transform: rotateY(90deg) translateZ(50px); }
.cube-face.left   { transform: rotateY(-90deg) translateZ(50px); }
.cube-face.top    { transform: rotateX(90deg) translateZ(50px); }
.cube-face.bottom { transform: rotateX(-90deg) translateZ(50px); }

.tex-thumb {
    transition: transform 0.2s, border-color 0.2s;
}

.tex-thumb:hover {
    transform: scale(1.1);
}

.tex-thumb.active {
    border-color: var(--primary-color) !important;
}

/* Print / PDF Export Styles */
@page {
    size: A4;
    margin: 1cm;
}

@media print {
    body {
        background: #fff;
        color: #000;
    }

    /* Hide UI Elements */
    .sidebar,
    .btn,
    .interactive-demo,
    .dda-controls,
    .bres-controls,
    .btn-group,
    input,
    select,
    canvas,
    #page-compare,
    #page-exam-mode,
    #page-playground,
    #page-practice {
        display: none !important;
    }

    .app-container {
        display: block;
    }

    .content-area {
        padding: 0;
        margin: 0;
    }

    /* Only show the survival sheet (or active text content) */
    .page.active {
        display: block !important;
        page-break-inside: avoid;
    }

    .card {
        background: #fff;
        border: 1px solid #ccc;
        box-shadow: none;
        color: #000;
        page-break-inside: avoid;
    }

    pre, code {
        background: #f0f0f0 !important;
        color: #000 !important;
        border: 1px solid #ccc;
    }

    h1, h2, h3, h4, p, li {
        color: #000 !important;
    }
}

/* Mobile Responsiveness */
@media (max-width: 768px) {
    .sidebar {
        position: fixed;
        left: -260px;
        height: 100vh;
        box-shadow: 2px 0 10px rgba(0,0,0,0.5);
    }

    .sidebar.open {
        left: 0;
    }

    .mobile-menu-btn {
        display: flex;
    }

    .content-area {
        padding: 20px;
    }

    .theory-grid {
        grid-template-columns: 1fr !important;
    }

    .page-header h1 {
        font-size: 1.6rem;
    }

    canvas {
        max-width: 100%;
        height: auto !important;
    }

    .card {
        padding: 15px;
    }
    
    .demo-container {
        flex-direction: column;
        gap: 20px;
    }
}