/* ============================================
   OpenProblems.ai — Design System
   A dark academic aesthetic with geometric precision
   ============================================ */

:root {
    /* Core palette - deep cosmic tones */
    --bg-deep: #0a0b0f;
    --bg-surface: #12141a;
    --bg-elevated: #1a1d26;
    --bg-hover: #22262f;
    
    /* Text hierarchy */
    --text-primary: #e8e6e3;
    --text-secondary: #9a9590;
    --text-muted: #5a5550;
    
    /* Branch accent colors */
    --color-math: #e6b450;
    --color-physics: #50a0e6;
    --color-bio: #50e6a0;
    --color-chem: #e65090;
    
    /* Functional */
    --color-open: #e65050;
    --color-partial: #e6b450;
    --color-solved: #50e6a0;
    
    /* Typography */
    --font-serif: 'Crimson Pro', Georgia, serif;
    --font-mono: 'JetBrains Mono', 'Fira Code', monospace;
    
    /* Spacing */
    --space-xs: 0.25rem;
    --space-sm: 0.5rem;
    --space-md: 1rem;
    --space-lg: 2rem;
    --space-xl: 4rem;
    --space-2xl: 8rem;
    
    /* Grid lines */
    --grid-color: rgba(255, 255, 255, 0.03);
}

/* Reset & Base */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    font-size: 18px;
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-serif);
    background: var(--bg-deep);
    color: var(--text-primary);
    line-height: 1.7;
    overflow-x: hidden;
}

/* Grid Background */
.grid-bg {
    position: fixed;
    inset: 0;
    background-image: 
        linear-gradient(var(--grid-color) 1px, transparent 1px),
        linear-gradient(90deg, var(--grid-color) 1px, transparent 1px);
    background-size: 60px 60px;
    pointer-events: none;
    z-index: -1;
}

.grid-bg::after {
    content: '';
    position: absolute;
    inset: 0;
    background: radial-gradient(ellipse at 50% 0%, rgba(230, 180, 80, 0.05) 0%, transparent 60%);
}

/* Typography */
h1, h2, h3, h4 {
    font-weight: 600;
    line-height: 1.2;
    letter-spacing: -0.02em;
}

em {
    font-style: italic;
    color: var(--color-math);
}

a {
    color: inherit;
    text-decoration: none;
    transition: color 0.2s ease;
}

/* Navigation */
.nav {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--space-md) var(--space-xl);
    background: rgba(10, 11, 15, 0.85);
    backdrop-filter: blur(12px);
    border-bottom: 1px solid rgba(255, 255, 255, 0.05);
    z-index: 1000;
}

.nav-logo {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    font-family: var(--font-mono);
    font-size: 1rem;
    font-weight: 500;
}

.logo-symbol {
    font-size: 1.5rem;
    color: var(--color-math);
}

.nav-links {
    display: flex;
    gap: var(--space-lg);
}

.nav-links a {
    font-family: var(--font-mono);
    font-size: 0.8rem;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--text-secondary);
    transition: color 0.2s ease;
}

.nav-links a:hover {
    color: var(--text-primary);
}

/* Hero Section */
.hero {
    min-height: 100vh;
    display: grid;
    grid-template-columns: 1.2fr 1fr;
    align-items: center;
    padding: var(--space-2xl) var(--space-xl);
    gap: var(--space-xl);
}

.hero-tagline {
    font-family: var(--font-mono);
    font-size: 0.75rem;
    text-transform: uppercase;
    letter-spacing: 0.3em;
    color: var(--color-math);
    margin-bottom: var(--space-md);
}

.hero-title {
    font-size: clamp(2.5rem, 5vw, 4rem);
    margin-bottom: var(--space-lg);
    max-width: 14ch;
}

.hero-description {
    font-size: 1.1rem;
    color: var(--text-secondary);
    margin-bottom: var(--space-xl);
    max-width: 40ch;
}

.hero-description .highlight {
    display: block;
    margin-top: var(--space-md);
    color: var(--text-primary);
    font-weight: 600;
}

.hero-cta {
    display: flex;
    gap: var(--space-md);
}

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: var(--space-md) var(--space-lg);
    font-family: var(--font-mono);
    font-size: 0.85rem;
    font-weight: 500;
    letter-spacing: 0.05em;
    border: 1px solid transparent;
    cursor: pointer;
    transition: all 0.3s ease;
}

.btn-primary {
    background: var(--color-math);
    color: var(--bg-deep);
}

.btn-primary:hover {
    background: #f0c060;
    transform: translateY(-2px);
    box-shadow: 0 4px 20px rgba(230, 180, 80, 0.3);
}

.btn-secondary {
    background: transparent;
    border-color: var(--text-muted);
    color: var(--text-primary);
}

.btn-secondary:hover {
    border-color: var(--text-primary);
    background: var(--bg-elevated);
}

/* Hero Visual - Orbital Animation */
.hero-visual {
    position: relative;
    width: 100%;
    aspect-ratio: 1;
    max-width: 500px;
    justify-self: center;
}

.orbit {
    position: absolute;
    border: 1px solid var(--grid-color);
    border-radius: 50%;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

.orbit::before {
    content: '';
    position: absolute;
    width: 12px;
    height: 12px;
    border-radius: 50%;
    top: 0;
    left: 50%;
    transform: translate(-50%, -50%);
}

.orbit-1 {
    width: 60%;
    height: 60%;
    animation: orbit-rotate 20s linear infinite;
}
.orbit-1::before { background: var(--color-math); }

.orbit-2 {
    width: 80%;
    height: 80%;
    animation: orbit-rotate 30s linear infinite reverse;
}
.orbit-2::before { background: var(--color-physics); }

.orbit-3 {
    width: 100%;
    height: 100%;
    animation: orbit-rotate 45s linear infinite;
}
.orbit-3::before { background: var(--color-bio); }

@keyframes orbit-rotate {
    from { transform: translate(-50%, -50%) rotate(0deg); }
    to { transform: translate(-50%, -50%) rotate(360deg); }
}

.central-node {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    width: 80px;
    height: 80px;
    background: var(--bg-surface);
    border: 2px solid var(--color-math);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 2.5rem;
    font-weight: 700;
    color: var(--color-math);
    box-shadow: 
        0 0 40px rgba(230, 180, 80, 0.2),
        inset 0 0 20px rgba(230, 180, 80, 0.1);
}

/* Sections */
section {
    padding: var(--space-2xl) var(--space-xl);
}

.section-title {
    font-size: clamp(2rem, 4vw, 3rem);
    text-align: center;
    margin-bottom: var(--space-sm);
}

.section-subtitle {
    text-align: center;
    color: var(--text-secondary);
    font-size: 1.1rem;
    max-width: 50ch;
    margin: 0 auto var(--space-xl);
}

/* Branches Grid */
.branch-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: var(--space-lg);
    max-width: 1400px;
    margin: 0 auto;
}

.branch-card {
    background: var(--bg-surface);
    border: 1px solid rgba(255, 255, 255, 0.05);
    padding: var(--space-xl);
    position: relative;
    overflow: hidden;
    transition: all 0.3s ease;
}

.branch-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 3px;
}

.branch-math::before { background: var(--color-math); }
.branch-physics::before { background: var(--color-physics); }
.branch-bio::before { background: var(--color-bio); }
.branch-chem::before { background: var(--color-chem); }

.branch-card:hover {
    transform: translateY(-4px);
    border-color: rgba(255, 255, 255, 0.1);
    box-shadow: 0 20px 40px rgba(0, 0, 0, 0.3);
}

.branch-icon {
    font-size: 3rem;
    margin-bottom: var(--space-md);
    opacity: 0.9;
}

.branch-math .branch-icon { color: var(--color-math); }
.branch-physics .branch-icon { color: var(--color-physics); }
.branch-bio .branch-icon { color: var(--color-bio); }
.branch-chem .branch-icon { color: var(--color-chem); }

.branch-card h3 {
    font-size: 1.5rem;
    margin-bottom: var(--space-xs);
}

.branch-count {
    font-family: var(--font-mono);
    font-size: 0.8rem;
    color: var(--text-muted);
    margin-bottom: var(--space-lg);
}

.branch-examples {
    list-style: none;
    margin-bottom: var(--space-lg);
}

.branch-examples li {
    font-size: 0.95rem;
    color: var(--text-secondary);
    padding: var(--space-xs) 0;
    border-bottom: 1px solid rgba(255, 255, 255, 0.03);
}

.branch-examples li:last-child {
    border-bottom: none;
}

.branch-link {
    font-family: var(--font-mono);
    font-size: 0.85rem;
    letter-spacing: 0.05em;
}

.branch-math .branch-link { color: var(--color-math); }
.branch-physics .branch-link { color: var(--color-physics); }
.branch-bio .branch-link { color: var(--color-bio); }
.branch-chem .branch-link { color: var(--color-chem); }

/* Featured Problems */
.featured-problems {
    background: var(--bg-surface);
}

.problems-list {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(400px, 1fr));
    gap: var(--space-lg);
    max-width: 1400px;
    margin: 0 auto var(--space-xl);
}

.problem-card {
    background: var(--bg-deep);
    border: 1px solid rgba(255, 255, 255, 0.05);
    padding: var(--space-lg);
    transition: all 0.3s ease;
}

.problem-card:hover {
    border-color: rgba(255, 255, 255, 0.1);
}

.problem-meta {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--space-md);
}

.problem-branch {
    font-family: var(--font-mono);
    font-size: 0.7rem;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    padding: var(--space-xs) var(--space-sm);
    border-radius: 2px;
}

.branch-tag-math { background: rgba(230, 180, 80, 0.15); color: var(--color-math); }
.branch-tag-physics { background: rgba(80, 160, 230, 0.15); color: var(--color-physics); }
.branch-tag-bio { background: rgba(80, 230, 160, 0.15); color: var(--color-bio); }
.branch-tag-chem { background: rgba(230, 80, 144, 0.15); color: var(--color-chem); }

.problem-age {
    font-family: var(--font-mono);
    font-size: 0.75rem;
    color: var(--text-muted);
}

.problem-title {
    font-size: 1.3rem;
    margin-bottom: var(--space-sm);
}

.problem-description {
    font-size: 0.95rem;
    color: var(--text-secondary);
    margin-bottom: var(--space-md);
}

.problem-status {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    font-family: var(--font-mono);
    font-size: 0.8rem;
    color: var(--text-muted);
}

.status-dot {
    width: 8px;
    height: 8px;
    border-radius: 50%;
}

.status-open { background: var(--color-open); }
.status-partial { background: var(--color-partial); }
.status-solved { background: var(--color-solved); }

.view-all-link {
    display: block;
    text-align: center;
    font-family: var(--font-mono);
    font-size: 0.9rem;
    color: var(--color-math);
}

.view-all-link:hover {
    text-decoration: underline;
}

/* Agents Section */
.agents-section {
    background: linear-gradient(180deg, var(--bg-deep) 0%, var(--bg-surface) 100%);
    text-align: center;
}

.agents-content {
    max-width: 800px;
    margin: 0 auto;
}

.agents-description {
    margin-bottom: var(--space-xl);
}

.agents-description p {
    color: var(--text-secondary);
    margin-bottom: var(--space-md);
}

.agent-stats {
    display: flex;
    justify-content: center;
    gap: var(--space-xl);
    margin-bottom: var(--space-xl);
    flex-wrap: wrap;
}

.stat {
    display: flex;
    flex-direction: column;
    align-items: center;
}

.stat-number {
    font-size: 3rem;
    font-weight: 700;
    color: var(--color-math);
    font-family: var(--font-mono);
}

.stat-label {
    font-family: var(--font-mono);
    font-size: 0.75rem;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--text-muted);
}

/* About Section */
.about-section {
    background: var(--bg-surface);
}

.about-content {
    max-width: 700px;
    margin: 0 auto;
    text-align: center;
}

.manifesto {
    font-size: 1.4rem;
    font-style: italic;
    color: var(--text-primary);
    margin-bottom: var(--space-xl);
    padding: var(--space-lg);
    border-left: 3px solid var(--color-math);
    text-align: left;
    background: rgba(230, 180, 80, 0.03);
}

.about-content > p {
    color: var(--text-secondary);
    margin-bottom: var(--space-md);
}

.about-content a {
    color: var(--color-math);
    text-decoration: underline;
}

/* Footer */
.footer {
    background: var(--bg-deep);
    padding: var(--space-xl);
    text-align: center;
    border-top: 1px solid rgba(255, 255, 255, 0.05);
}

.footer-content {
    max-width: 600px;
    margin: 0 auto;
}

.footer-logo {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--space-sm);
    font-family: var(--font-mono);
    font-size: 1.1rem;
    margin-bottom: var(--space-sm);
}

.footer-tagline {
    color: var(--text-muted);
    font-size: 0.9rem;
    margin-bottom: var(--space-lg);
}

.footer-links {
    display: flex;
    justify-content: center;
    gap: var(--space-lg);
    margin-bottom: var(--space-lg);
}

.footer-links a {
    font-family: var(--font-mono);
    font-size: 0.8rem;
    color: var(--text-secondary);
}

.footer-links a:hover {
    color: var(--text-primary);
}

.footer-copy {
    font-family: var(--font-mono);
    font-size: 0.75rem;
    color: var(--text-muted);
}

/* Responsive */
@media (max-width: 900px) {
    .hero {
        grid-template-columns: 1fr;
        text-align: center;
        padding-top: 120px;
    }
    
    .hero-title {
        max-width: none;
    }
    
    .hero-description {
        max-width: none;
        margin-left: auto;
        margin-right: auto;
    }
    
    .hero-cta {
        justify-content: center;
    }
    
    .hero-visual {
        max-width: 350px;
        order: -1;
    }
    
    .nav {
        padding: var(--space-md);
    }
    
    .nav-links {
        gap: var(--space-md);
    }
    
    section {
        padding: var(--space-xl) var(--space-md);
    }
    
    .problems-list {
        grid-template-columns: 1fr;
    }
    
    .agent-stats {
        gap: var(--space-lg);
    }
}

@media (max-width: 600px) {
    html {
        font-size: 16px;
    }
    
    .nav-links {
        display: none;
    }
    
    .hero-cta {
        flex-direction: column;
    }
    
    .btn {
        width: 100%;
    }
}

/* Animations */
@keyframes fade-in-up {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.hero-content > * {
    animation: fade-in-up 0.8s ease backwards;
}

.hero-tagline { animation-delay: 0.1s; }
.hero-title { animation-delay: 0.2s; }
.hero-description { animation-delay: 0.3s; }
.hero-cta { animation-delay: 0.4s; }

.branch-card {
    animation: fade-in-up 0.6s ease backwards;
}

.branch-card:nth-child(1) { animation-delay: 0.1s; }
.branch-card:nth-child(2) { animation-delay: 0.2s; }
.branch-card:nth-child(3) { animation-delay: 0.3s; }
.branch-card:nth-child(4) { animation-delay: 0.4s; }