:root {
    /* Color Variables */
    --color-primary: #4ECDC4;
    --color-secondary: #45B7D1;
    --color-accent: #F39C12;
    --color-danger: #FF6B6B;
    --color-success: #96CEB4;
    --color-warning: #F7DC6F;

    --color-background: #0f172a;
    --color-surface: #1e293b;
    --color-surface-light: #334155;
    --color-text: #f8fafc;
    --color-text-muted: #94a3b8;
    --color-border: #475569;

    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-xxl: 3rem;

    /* Typography */
    --font-primary: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
    --font-mono: 'JetBrains Mono', 'Fira Code', monospace;

    /* Shadows */
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1);

    /* Border Radius */
    --radius-sm: 0.375rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --radius-xl: 1rem;

    /* Transitions */
    --transition-fast: 0.15s ease-in-out;
    --transition-normal: 0.25s ease-in-out;
    --transition-slow: 0.4s ease-in-out;
}

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

html {
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-primary);
    background: var(--color-background);
    color: var(--color-text);
    line-height: 1.6;
    overflow-x: hidden;
}

.container {
    max-width: 1400px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
}

/* Header */
.header {
    background: var(--color-surface);
    border-bottom: 1px solid var(--color-border);
    padding: var(--spacing-lg) 0;
    position: sticky;
    top: 0;
    z-index: 100;
    backdrop-filter: blur(10px);
}

.header__content {
    text-align: center;
}

.header__logo {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-md);
}

.logo-icon {
    width: 48px;
    height: 48px;
    filter: drop-shadow(0 4px 8px rgba(0, 0, 0, 0.2));
}

.header__title {
    font-size: 2.5rem;
    font-weight: 800;
    background: linear-gradient(135deg, var(--color-primary), var(--color-secondary));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.header__subtitle {
    font-size: 1.125rem;
    color: var(--color-text-muted);
    margin-bottom: var(--spacing-lg);
}

.header__stats {
    display: flex;
    justify-content: center;
    gap: var(--spacing-xl);
    flex-wrap: wrap;
}

.stat {
    text-align: center;
}

.stat__number {
    display: block;
    font-size: 2rem;
    font-weight: 700;
    color: var(--color-primary);
}

.stat__label {
    font-size: 0.875rem;
    color: var(--color-text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

/* Navigation */
.navigation {
    background: var(--color-surface-light);
    border-bottom: 1px solid var(--color-border);
    padding: var(--spacing-md) 0;
    position: sticky;
    top: 0;
    z-index: 99;
}

.navigation .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: var(--spacing-md);
}

.nav__tabs {
    display: flex;
    gap: var(--spacing-sm);
    flex-wrap: wrap;
}

.nav__tab {
    background: none;
    border: 2px solid transparent;
    color: var(--color-text-muted);
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: var(--radius-lg);
    cursor: pointer;
    transition: all var(--transition-normal);
    font-weight: 500;
    white-space: nowrap;
}

.nav__tab:hover {
    color: var(--color-text);
    background: rgba(255, 255, 255, 0.05);
}

.nav__tab--active {
    color: var(--color-primary);
    border-color: var(--color-primary);
    background: rgba(78, 205, 196, 0.1);
}

.nav__controls {
    display: flex;
    gap: var(--spacing-md);
    flex-wrap: wrap;
}

.search-input,
.filter-select {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    color: var(--color-text);
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: var(--radius-md);
    transition: border-color var(--transition-normal);
}

.search-input:focus,
.filter-select:focus {
    outline: none;
    border-color: var(--color-primary);
}

/* Main Content */
.main {
    min-height: 80vh;
    padding: var(--spacing-xl) 0;
}

.content-section {
    display: none;
}

.content-section--active {
    display: block;
}

.section-title {
    font-size: 2.25rem;
    font-weight: 700;
    text-align: center;
    margin-bottom: var(--spacing-md);
    background: linear-gradient(135deg, var(--color-text), var(--color-text-muted));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.section-subtitle {
    text-align: center;
    color: var(--color-text-muted);
    font-size: 1.125rem;
    margin-bottom: var(--spacing-xxl);
}

/* Flowchart */
.flowchart-container {
    background: var(--color-surface);
    border-radius: var(--radius-xl);
    padding: var(--spacing-xl);
    box-shadow: var(--shadow-xl);
}

.flowchart-canvas {
    background: linear-gradient(135deg, #0f172a 0%, #1e293b 100%);
    border-radius: var(--radius-lg);
    min-height: 800px;
    position: relative;
    overflow: hidden;
    border: 2px solid var(--color-border);
}

.flowchart-controls {
    display: flex;
    justify-content: center;
    gap: var(--spacing-md);
    margin-top: var(--spacing-lg);
    flex-wrap: wrap;
}

.control-btn {
    background: var(--color-primary);
    color: white;
    border: none;
    padding: var(--spacing-sm) var(--spacing-lg);
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-normal);
    font-weight: 500;
}

.control-btn:hover {
    background: var(--color-secondary);
    transform: translateY(-1px);
}

.chapter-counter {
    text-align: center;
    margin-top: var(--spacing-md);
    color: var(--color-text-muted);
    font-weight: 500;
}

/* Flowchart SVG Styles */
.flowchart-svg {
    width: 100%;
    height: 100%;
    min-height: 800px;
}

.flowchart-node {
    cursor: pointer;
    transition: all var(--transition-normal);
}

.flowchart-node:hover .node-circle {
    r: 35;
    stroke-width: 4;
}

.flowchart-node:hover .node-label {
    font-size: 16px;
    font-weight: 700;
}

.flowchart-connection {
    stroke: var(--color-primary);
    stroke-width: 2;
    fill: none;
    opacity: 0.6;
    transition: all var(--transition-normal);
}

.flowchart-connection:hover {
    opacity: 1;
    stroke-width: 3;
}

.node-circle {
    transition: all var(--transition-normal);
    filter: drop-shadow(0 4px 8px rgba(0, 0, 0, 0.3));
}

.node-label {
    fill: var(--color-text);
    font-size: 14px;
    font-weight: 600;
    text-anchor: middle;
    pointer-events: none;
    transition: all var(--transition-normal);
}

.node-title {
    fill: var(--color-text-muted);
    font-size: 12px;
    font-weight: 500;
    text-anchor: middle;
    pointer-events: none;
}

/* Timeline */
.timeline-container {
    position: relative;
}

.timeline {
    position: relative;
    padding: var(--spacing-lg) 0;
}

.timeline::before {
    content: '';
    position: absolute;
    left: 50%;
    transform: translateX(-50%);
    width: 4px;
    height: 100%;
    background: linear-gradient(180deg, var(--color-primary), var(--color-secondary));
    border-radius: 2px;
}

.timeline-item {
    display: flex;
    align-items: center;
    margin-bottom: var(--spacing-xl);
    position: relative;
}

.timeline-item:nth-child(odd) {
    flex-direction: row-reverse;
}

.timeline-item:nth-child(odd) .timeline-content {
    margin-left: 0;
    margin-right: var(--spacing-xl);
    text-align: right;
}

.timeline-marker {
    width: 20px;
    height: 20px;
    background: var(--color-primary);
    border-radius: 50%;
    position: absolute;
    left: 50%;
    transform: translateX(-50%);
    z-index: 10;
    box-shadow: 0 0 0 4px var(--color-background), 0 0 0 8px var(--color-primary);
}

.timeline-content {
    background: var(--color-surface);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    margin-left: var(--spacing-xl);
    width: 45%;
    box-shadow: var(--shadow-lg);
    cursor: pointer;
    transition: all var(--transition-normal);
}

.timeline-content:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-xl);
}

.timeline-chapter {
    font-size: 0.875rem;
    color: var(--color-primary);
    font-weight: 600;
    margin-bottom: var(--spacing-xs);
}

.timeline-title {
    font-size: 1.25rem;
    font-weight: 700;
    margin-bottom: var(--spacing-sm);
}

.timeline-problem {
    color: var(--color-text-muted);
    font-size: 0.925rem;
    margin-bottom: var(--spacing-sm);
}

.timeline-tech {
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-xs);
}

.tech-tag {
    background: rgba(78, 205, 196, 0.2);
    color: var(--color-primary);
    padding: var(--spacing-xs) var(--spacing-sm);
    border-radius: var(--radius-sm);
    font-size: 0.75rem;
    font-weight: 500;
}

/* Theory Grid */
.theory-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(350px, 1fr));
    gap: var(--spacing-xl);
}

.theory-card {
    background: var(--color-surface);
    padding: var(--spacing-xl);
    border-radius: var(--radius-xl);
    box-shadow: var(--shadow-lg);
    transition: all var(--transition-normal);
}

.theory-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-xl);
}

.theory-header {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-lg);
}

.theory-icon {
    width: 48px;
    height: 48px;
    background: linear-gradient(135deg, var(--color-primary), var(--color-secondary));
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.5rem;
}

.theory-title {
    font-size: 1.375rem;
    font-weight: 700;
}

.theory-description {
    color: var(--color-text-muted);
    line-height: 1.7;
    margin-bottom: var(--spacing-lg);
}

.theory-applications {
    background: rgba(78, 205, 196, 0.05);
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
    border-left: 4px solid var(--color-primary);
}

.theory-applications h4 {
    color: var(--color-primary);
    font-size: 0.875rem;
    font-weight: 600;
    margin-bottom: var(--spacing-sm);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

/* Architecture Timeline */
.architecture-timeline {
    display: grid;
    gap: var(--spacing-xl);
}

.architecture-stage {
    background: var(--color-surface);
    border-radius: var(--radius-xl);
    padding: var(--spacing-xl);
    box-shadow: var(--shadow-lg);
}

.stage-header {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-lg);
}

.stage-number {
    background: var(--color-primary);
    color: white;
    width: 40px;
    height: 40px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 700;
}

.stage-title {
    font-size: 1.5rem;
    font-weight: 700;
}

.architecture-comparison {
    display: grid;
    grid-template-columns: 1fr auto 1fr;
    gap: var(--spacing-lg);
    align-items: center;
    margin: var(--spacing-lg) 0;
}

.architecture-box {
    background: var(--color-background);
    padding: var(--spacing-lg);
    border-radius: var(--radius-md);
    border: 2px solid var(--color-border);
}

.architecture-box h4 {
    color: var(--color-accent);
    margin-bottom: var(--spacing-md);
    text-align: center;
    font-weight: 600;
}

.architecture-arrow {
    font-size: 2rem;
    color: var(--color-primary);
}

/* Modal */
.modal {
    display: none;
    position: fixed;
    z-index: 1000;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.8);
    backdrop-filter: blur(4px);
}

.modal-content {
    background: var(--color-surface);
    margin: 2% auto;
    padding: 0;
    border-radius: var(--radius-xl);
    max-width: 900px;
    max-height: 90vh;
    overflow-y: auto;
    position: relative;
    box-shadow: var(--shadow-xl);
}

.modal-close {
    position: absolute;
    top: var(--spacing-md);
    right: var(--spacing-md);
    background: var(--color-danger);
    color: white;
    border: none;
    width: 32px;
    height: 32px;
    border-radius: 50%;
    cursor: pointer;
    font-size: 1.25rem;
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 10;
}

.modal-body {
    padding: var(--spacing-xxl);
}

/* Chapter Detail Styles */
.chapter-detail {
    text-align: left;
}

.chapter-header {
    text-align: center;
    margin-bottom: var(--spacing-xxl);
    padding-bottom: var(--spacing-xl);
    border-bottom: 2px solid var(--color-border);
}

.chapter-icon {
    font-size: 4rem;
    margin-bottom: var(--spacing-md);
}

.chapter-title {
    font-size: 2rem;
    font-weight: 800;
    margin-bottom: var(--spacing-sm);
}

.chapter-subtitle {
    color: var(--color-text-muted);
    font-size: 1.25rem;
}

.chapter-section {
    margin-bottom: var(--spacing-xl);
}

.chapter-section h3 {
    font-size: 1.25rem;
    font-weight: 700;
    margin-bottom: var(--spacing-md);
    color: var(--color-primary);
}

.chapter-section p {
    line-height: 1.7;
    margin-bottom: var(--spacing-md);
}

.chapter-section ul {
    padding-left: var(--spacing-lg);
}

.chapter-section li {
    margin-bottom: var(--spacing-sm);
    color: var(--color-text-muted);
}

.metrics-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--spacing-md);
    margin: var(--spacing-lg) 0;
}

.metric-item {
    background: var(--color-background);
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
    text-align: center;
    border: 1px solid var(--color-border);
}

.metric-value {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--color-success);
}

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

/* Footer */
.footer {
    background: var(--color-surface);
    border-top: 1px solid var(--color-border);
    padding: var(--spacing-xl) 0;
    text-align: center;
    color: var(--color-text-muted);
}

/* Responsive Design */
@media (max-width: 768px) {
    .container {
        padding: 0 var(--spacing-sm);
    }

    .header__title {
        font-size: 2rem;
    }

    .header__stats {
        gap: var(--spacing-md);
    }

    .navigation .container {
        flex-direction: column;
        align-items: stretch;
    }

    .nav__tabs {
        justify-content: center;
        flex-wrap: wrap;
    }

    .nav__controls {
        justify-content: center;
        flex-wrap: wrap;
    }

    .flowchart-canvas {
        min-height: 600px;
    }

    .timeline::before {
        left: 20px;
    }

    .timeline-item {
        flex-direction: row !important;
        padding-left: 50px;
    }

    .timeline-marker {
        left: 20px;
    }

    .timeline-content {
        width: 100%;
        margin: 0;
        text-align: left !important;
    }

    .architecture-comparison {
        grid-template-columns: 1fr;
        gap: var(--spacing-md);
    }

    .architecture-arrow {
        transform: rotate(90deg);
        align-self: center;
    }

    .metrics-grid {
        grid-template-columns: 1fr;
    }

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

    .modal-content {
        margin: 5% auto;
        max-width: 95%;
    }

    .modal-body {
        padding: var(--spacing-lg);
    }

    .section-title {
        font-size: 1.75rem;
    }
}

/* Animation Classes */
.fade-in {
    animation: fadeIn 0.5s ease-in-out;
}

@keyframes fadeIn {
    from { 
        opacity: 0; 
        transform: translateY(20px); 
    }
    to { 
        opacity: 1; 
        transform: translateY(0); 
    }
}

.pulse {
    animation: pulse 2s infinite;
}

@keyframes pulse {
    0%, 100% { 
        opacity: 1; 
    }
    50% { 
        opacity: 0.7; 
    }
}

.bounce-in {
    animation: bounceIn 0.6s ease-out;
}

@keyframes bounceIn {
    0% {
        opacity: 0;
        transform: scale(0.3);
    }
    50% {
        opacity: 1;
        transform: scale(1.05);
    }
    70% {
        transform: scale(0.9);
    }
    100% {
        opacity: 1;
        transform: scale(1);
    }
}