/* ============================================
   Control Theory Interactive Learning - Styles
   ============================================ */

:root {
    --bg-primary: #0d1117;
    --bg-secondary: #161b22;
    --bg-tertiary: #21262d;
    --text-primary: #e6edf3;
    --text-secondary: #8b949e;
    --text-muted: #6e7681;
    --accent-blue: #58a6ff;
    --accent-green: #3fb950;
    --accent-purple: #a371f7;
    --accent-orange: #d29922;
    --accent-red: #f85149;
    --border-color: #30363d;
    --card-bg: #161b22;
    --code-bg: #1c2128;
}

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

html {
    scroll-behavior: smooth;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
}

/* Navigation */
.main-nav {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem 2rem;
    background: rgba(13, 17, 23, 0.9);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--border-color);
    z-index: 1000;
}

.nav-brand {
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--text-primary);
}

.nav-links {
    display: flex;
    gap: 2rem;
}

.nav-links a {
    color: var(--text-secondary);
    text-decoration: none;
    font-size: 0.95rem;
    transition: color 0.2s;
}

.nav-links a:hover,
.nav-links a.active {
    color: var(--accent-blue);
}

/* Module Navigation */
.module-nav {
    display: flex;
    gap: 1rem;
    align-items: center;
}

.module-nav a {
    color: var(--text-secondary);
    text-decoration: none;
    padding: 0.5rem 1rem;
    border-radius: 6px;
    font-size: 0.9rem;
    transition: all 0.2s;
}

.module-nav a:hover {
    background: var(--bg-tertiary);
    color: var(--text-primary);
}

.module-nav .nav-arrow {
    font-size: 1.2rem;
}

/* Hero Section */
.hero {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 4rem;
    padding: 8rem 4rem 4rem;
    max-width: 1400px;
    margin: 0 auto;
    min-height: 80vh;
    align-items: center;
}

.hero-content h1 {
    font-size: 3.5rem;
    font-weight: 700;
    margin-bottom: 1rem;
    background: linear-gradient(135deg, var(--accent-blue), var(--accent-purple));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.subtitle {
    font-size: 1.5rem;
    color: var(--text-secondary);
    margin-bottom: 1.5rem;
}

.description {
    font-size: 1.1rem;
    color: var(--text-secondary);
    max-width: 500px;
    margin-bottom: 2rem;
}

.cta-button {
    display: inline-block;
    padding: 1rem 2rem;
    background: var(--accent-blue);
    color: var(--bg-primary);
    text-decoration: none;
    border-radius: 8px;
    font-weight: 600;
    font-size: 1.1rem;
    transition: all 0.2s;
}

.cta-button:hover {
    background: #79b8ff;
    transform: translateY(-2px);
}

.hero-visual {
    background: var(--bg-secondary);
    border-radius: 12px;
    border: 1px solid var(--border-color);
    overflow: hidden;
}

#heroCanvas {
    width: 100%;
    height: 400px;
}

/* Main Content */
main {
    max-width: 1200px;
    margin: 0 auto;
    padding: 2rem;
}

section {
    margin-bottom: 4rem;
}

h2 {
    font-size: 2rem;
    margin-bottom: 1rem;
    color: var(--text-primary);
}

.section-intro {
    color: var(--text-secondary);
    font-size: 1.1rem;
    margin-bottom: 2rem;
}

/* Intro Section */
.intro-section {
    padding: 4rem 0;
}

.intro-grid {
    display: grid;
    grid-template-columns: 1fr 1.2fr;
    gap: 3rem;
    align-items: center;
}

.intro-text p {
    color: var(--text-secondary);
    font-size: 1.1rem;
    margin-bottom: 1rem;
}

.intro-text strong {
    color: var(--text-primary);
}

/* Feedback Loop Diagram */
.feedback-loop {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    padding: 2rem;
    background: var(--bg-secondary);
    border-radius: 12px;
    border: 1px solid var(--border-color);
    position: relative;
}

.block {
    padding: 1rem 1.5rem;
    border-radius: 8px;
    text-align: center;
    font-weight: 500;
    font-size: 0.9rem;
}

.block .small {
    display: block;
    font-size: 0.75rem;
    font-weight: 400;
    opacity: 0.7;
    margin-top: 0.25rem;
}

.block.reference {
    background: var(--accent-green);
    color: var(--bg-primary);
}

.block.controller {
    background: var(--accent-blue);
    color: var(--bg-primary);
}

.block.plant {
    background: var(--accent-purple);
    color: white;
}

.block.output {
    background: var(--accent-orange);
    color: var(--bg-primary);
}

.arrow {
    color: var(--text-muted);
    font-size: 1.5rem;
}

.feedback-line {
    position: absolute;
    bottom: 0.5rem;
    left: 15%;
    right: 15%;
    height: 2px;
    background: var(--text-muted);
}

.feedback-line::before,
.feedback-line::after {
    content: '';
    position: absolute;
    width: 2px;
    height: 20px;
    background: var(--text-muted);
}

.feedback-line::before {
    left: 0;
    bottom: 0;
}

.feedback-line::after {
    right: 0;
    bottom: 0;
}

.feedback-label {
    position: absolute;
    bottom: 0.75rem;
    left: 50%;
    transform: translateX(-50%);
    font-size: 0.8rem;
    color: var(--text-muted);
    background: var(--bg-secondary);
    padding: 0 0.5rem;
}

/* Roadmap */
.roadmap-section {
    padding: 2rem 0;
}

.roadmap-part {
    margin-bottom: 3rem;
}

.part-title {
    font-size: 1.3rem;
    color: var(--accent-blue);
    margin-bottom: 1.5rem;
    padding-bottom: 0.5rem;
    border-bottom: 1px solid var(--border-color);
}

.modules-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
    gap: 1.5rem;
}

.module-card {
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 1.5rem;
    display: flex;
    flex-direction: column;
    gap: 1rem;
    transition: all 0.2s;
    text-decoration: none;
    color: inherit;
}

.module-card.available {
    cursor: pointer;
}

.module-card.available:hover {
    border-color: var(--accent-blue);
    transform: translateY(-2px);
    box-shadow: 0 4px 20px rgba(88, 166, 255, 0.1);
}

.module-card.locked {
    opacity: 0.6;
}

.module-number {
    font-size: 2rem;
    font-weight: 700;
    color: var(--accent-blue);
    opacity: 0.5;
}

.module-card.available .module-number {
    opacity: 1;
}

.module-content h4 {
    font-size: 1.1rem;
    margin-bottom: 0.5rem;
}

.module-content p {
    font-size: 0.9rem;
    color: var(--text-secondary);
}

.module-topics {
    list-style: none;
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
    margin-top: 0.5rem;
}

.module-topics li {
    font-size: 0.75rem;
    padding: 0.25rem 0.5rem;
    background: var(--bg-tertiary);
    border-radius: 4px;
    color: var(--text-muted);
}

.module-status {
    font-size: 0.8rem;
    color: var(--accent-green);
    margin-top: auto;
}

.module-card.locked .module-status {
    color: var(--text-muted);
}

/* Philosophy Section */
.philosophy-section {
    padding: 4rem 0;
}

.philosophy-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 1.5rem;
}

.philosophy-card {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 1.5rem;
    text-align: center;
}

.philosophy-icon {
    font-size: 2rem;
    margin-bottom: 1rem;
}

.philosophy-card h4 {
    margin-bottom: 0.5rem;
}

.philosophy-card p {
    font-size: 0.9rem;
    color: var(--text-secondary);
}

/* Footer */
footer {
    text-align: center;
    padding: 3rem 2rem;
    border-top: 1px solid var(--border-color);
    color: var(--text-muted);
}

/* ============================================
   Module Page Styles
   ============================================ */

.module-header {
    padding: 6rem 2rem 3rem;
    background: linear-gradient(180deg, var(--bg-secondary) 0%, var(--bg-primary) 100%);
    border-bottom: 1px solid var(--border-color);
}

.module-header-content {
    max-width: 900px;
    margin: 0 auto;
}

.module-label {
    display: inline-block;
    padding: 0.25rem 0.75rem;
    background: var(--accent-blue);
    color: var(--bg-primary);
    border-radius: 4px;
    font-size: 0.8rem;
    font-weight: 600;
    margin-bottom: 1rem;
}

.module-header h1 {
    font-size: 2.5rem;
    margin-bottom: 1rem;
}

.module-description {
    font-size: 1.2rem;
    color: var(--text-secondary);
    max-width: 700px;
}

.module-content-wrapper {
    max-width: 900px;
    margin: 0 auto;
    padding: 3rem 2rem;
}

/* Content Sections */
.content-section {
    margin-bottom: 4rem;
}

.content-section h2 {
    font-size: 1.75rem;
    margin-bottom: 1.5rem;
    padding-bottom: 0.5rem;
    border-bottom: 1px solid var(--border-color);
}

.content-section h3 {
    font-size: 1.3rem;
    margin: 2rem 0 1rem;
    color: var(--accent-blue);
}

.content-section p {
    margin-bottom: 1rem;
    color: var(--text-secondary);
    font-size: 1.05rem;
}

.content-section strong {
    color: var(--text-primary);
}

/* Concept Box */
.concept-box {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-left: 4px solid var(--accent-blue);
    border-radius: 8px;
    padding: 1.5rem;
    margin: 1.5rem 0;
}

.concept-box.insight {
    border-left-color: var(--accent-green);
}

.concept-box.warning {
    border-left-color: var(--accent-orange);
}

.concept-box h4 {
    margin-bottom: 0.75rem;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.concept-box p {
    margin-bottom: 0.5rem;
    color: var(--text-secondary);
}

.concept-box p:last-child {
    margin-bottom: 0;
}

/* Math Display */
.math-block {
    background: var(--code-bg);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    padding: 1.5rem;
    margin: 1.5rem 0;
    overflow-x: auto;
    text-align: center;
}

.math-inline {
    padding: 0.1rem 0.3rem;
    background: var(--code-bg);
    border-radius: 4px;
}

/* Interactive Demo Container */
.demo-container {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 1.5rem;
    margin: 2rem 0;
}

.demo-container h4 {
    margin-bottom: 1rem;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.demo-controls {
    display: flex;
    flex-wrap: wrap;
    gap: 1.5rem;
    margin-bottom: 1rem;
    padding: 1rem;
    background: var(--bg-tertiary);
    border-radius: 8px;
}

.control-group {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

.control-group label {
    font-size: 0.85rem;
    color: var(--text-secondary);
}

.control-group input[type="range"] {
    width: 150px;
    accent-color: var(--accent-blue);
}

.control-group .value-display {
    font-family: 'SF Mono', Monaco, monospace;
    font-size: 0.9rem;
    color: var(--accent-blue);
}

.demo-plot {
    width: 100%;
    height: 350px;
    background: var(--bg-primary);
    border-radius: 8px;
}

.demo-explanation {
    margin-top: 1rem;
    padding: 1rem;
    background: var(--bg-tertiary);
    border-radius: 8px;
    font-size: 0.95rem;
    color: var(--text-secondary);
}

/* Example Box */
.example-box {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    padding: 1.5rem;
    margin: 1.5rem 0;
}

.example-box h4 {
    color: var(--accent-purple);
    margin-bottom: 1rem;
}

.example-box ol,
.example-box ul {
    margin-left: 1.5rem;
    color: var(--text-secondary);
}

.example-box li {
    margin-bottom: 0.5rem;
}

/* Navigation Footer */
.module-footer {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 2rem 0;
    margin-top: 4rem;
    border-top: 1px solid var(--border-color);
}

.nav-button {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    padding: 1rem 1.5rem;
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    color: var(--text-primary);
    text-decoration: none;
    transition: all 0.2s;
}

.nav-button:hover {
    border-color: var(--accent-blue);
    background: var(--bg-tertiary);
}

.nav-button.next {
    background: var(--accent-blue);
    color: var(--bg-primary);
    border-color: var(--accent-blue);
}

.nav-button.next:hover {
    background: #79b8ff;
}

.nav-button .label {
    font-size: 0.8rem;
    color: var(--text-muted);
}

.nav-button.next .label {
    color: rgba(0, 0, 0, 0.6);
}

.nav-button .title {
    font-weight: 500;
}

/* Two Column Layout */
.two-column {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 2rem;
    margin: 1.5rem 0;
}

.column {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    padding: 1.5rem;
}

.column h4 {
    margin-bottom: 1rem;
    color: var(--accent-blue);
}

/* Responsive */
@media (max-width: 1024px) {
    .hero {
        grid-template-columns: 1fr;
        padding: 6rem 2rem 3rem;
        min-height: auto;
    }

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

    .philosophy-grid {
        grid-template-columns: repeat(2, 1fr);
    }

    .two-column {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 640px) {
    .hero-content h1 {
        font-size: 2.5rem;
    }

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

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

    .demo-controls {
        flex-direction: column;
    }
}