/* ========================================
   网事小栈 - 卫星互联网 × 算力网络
   Design System v1.0
   ======================================== */

/* CSS Variables */
:root {
    /* Colors */
    --bg-primary: #0a0a0f;
    --bg-secondary: #12121a;
    --bg-card: #1a1a24;
    --bg-card-hover: #22222e;
    
    --text-primary: #f0f0f5;
    --text-secondary: #a0a0b0;
    --text-muted: #6b6b7b;
    
    --accent-primary: #3b82f6;
    --accent-secondary: #8b5cf6;
    --accent-satellite: #22d3ee;
    --accent-compute: #a855f7;
    
    --border-color: #2a2a3a;
    --border-hover: #3a3a4a;
    
    /* Typography */
    --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    --font-mono: "SF Mono", "Fira Code", Consolas, monospace;
    
    /* Spacing */
    --space-xs: 0.25rem;
    --space-sm: 0.5rem;
    --space-md: 1rem;
    --space-lg: 1.5rem;
    --space-xl: 2rem;
    --space-2xl: 3rem;
    --space-3xl: 4rem;
    
    /* Border Radius */
    --radius-sm: 4px;
    --radius-md: 8px;
    --radius-lg: 12px;
    --radius-xl: 16px;
    
    /* Transitions */
    --transition-fast: 0.15s ease;
    --transition-normal: 0.25s ease;
    --transition-slow: 0.4s ease;
}

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

html {
    scroll-behavior: smooth;
    font-size: 16px;
}

body {
    font-family: var(--font-sans);
    background-color: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

a {
    color: var(--accent-primary);
    text-decoration: none;
    transition: color var(--transition-fast);
}

a:hover {
    color: var(--accent-satellite);
}

/* Container */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--space-lg);
}

/* ========================================
   Header / Navigation
   ======================================== */
.header {
    position: sticky;
    top: 0;
    z-index: 100;
    background: rgba(10, 10, 15, 0.9);
    backdrop-filter: blur(12px);
    border-bottom: 1px solid var(--border-color);
}

.nav {
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 64px;
}

.logo {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--text-primary);
}

.logo-icon {
    width: 32px;
    height: 32px;
    background: linear-gradient(135deg, var(--accent-satellite), var(--accent-primary));
    border-radius: var(--radius-sm);
    display: flex;
    align-items: center;
    justify-content: center;
}

.logo-icon svg {
    width: 20px;
    height: 20px;
    color: var(--bg-primary);
}

.nav-links {
    display: flex;
    align-items: center;
    gap: var(--space-xl);
    list-style: none;
}

.nav-links a {
    color: var(--text-secondary);
    font-size: 0.95rem;
    font-weight: 500;
    padding: var(--space-sm) 0;
    position: relative;
}

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

.nav-links a::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: 0;
    height: 2px;
    background: var(--accent-primary);
    transition: width var(--transition-normal);
}

.nav-links a:hover::after,
.nav-links a.active::after {
    width: 100%;
}

.nav-actions {
    display: flex;
    align-items: center;
    gap: var(--space-md);
}

.search-btn {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: var(--space-sm) var(--space-md);
    color: var(--text-secondary);
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    font-size: 0.875rem;
    transition: all var(--transition-fast);
}

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

.theme-toggle {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    width: 40px;
    height: 40px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    color: var(--text-secondary);
    transition: all var(--transition-fast);
}

.theme-toggle:hover {
    background: var(--bg-card-hover);
    color: var(--text-primary);
}

/* ========================================
   Hero Section
   ======================================== */
.hero {
    padding: var(--space-3xl) 0;
    text-align: center;
    position: relative;
    overflow: hidden;
}

.hero::before {
    content: '';
    position: absolute;
    top: 0;
    left: 50%;
    transform: translateX(-50%);
    width: 800px;
    height: 800px;
    background: radial-gradient(circle, rgba(59, 130, 246, 0.1) 0%, transparent 70%);
    pointer-events: none;
}

.hero-badge {
    display: inline-flex;
    align-items: center;
    gap: var(--space-sm);
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: 100px;
    padding: var(--space-xs) var(--space-md);
    font-size: 0.8rem;
    color: var(--text-secondary);
    margin-bottom: var(--space-lg);
}

.hero-badge-dot {
    width: 8px;
    height: 8px;
    background: var(--accent-satellite);
    border-radius: 50%;
    animation: pulse 2s infinite;
}

@keyframes pulse {
    0%, 100% { opacity: 1; }
    50% { opacity: 0.5; }
}

.hero h1 {
    font-size: clamp(2.5rem, 6vw, 4rem);
    font-weight: 800;
    line-height: 1.1;
    margin-bottom: var(--space-lg);
    background: linear-gradient(135deg, var(--text-primary) 0%, var(--text-secondary) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero-topics {
    display: flex;
    justify-content: center;
    gap: var(--space-lg);
    margin-bottom: var(--space-xl);
}

.hero-topic {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    font-size: 1.1rem;
    color: var(--text-secondary);
}

.hero-topic-icon {
    width: 40px;
    height: 40px;
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
}

.hero-topic-icon.satellite {
    background: rgba(34, 211, 238, 0.15);
    color: var(--accent-satellite);
}

.hero-topic-icon.compute {
    background: rgba(168, 85, 247, 0.15);
    color: var(--accent-compute);
}

.hero-description {
    font-size: 1.25rem;
    color: var(--text-secondary);
    max-width: 600px;
    margin: 0 auto var(--space-xl);
    line-height: 1.7;
}

.hero-actions {
    display: flex;
    justify-content: center;
    gap: var(--space-md);
}

.btn {
    display: inline-flex;
    align-items: center;
    gap: var(--space-sm);
    padding: var(--space-md) var(--space-xl);
    border-radius: var(--radius-md);
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-fast);
    border: none;
}

.btn-primary {
    background: var(--accent-primary);
    color: white;
}

.btn-primary:hover {
    background: #2563eb;
    transform: translateY(-2px);
    box-shadow: 0 4px 20px rgba(59, 130, 246, 0.4);
}

.btn-secondary {
    background: var(--bg-card);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
}

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

/* ========================================
   Section Styles
   ======================================== */
.section {
    padding: var(--space-3xl) 0;
}

.section-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: var(--space-xl);
}

.section-title {
    font-size: 1.5rem;
    font-weight: 700;
    display: flex;
    align-items: center;
    gap: var(--space-md);
}

.section-title-icon {
    width: 36px;
    height: 36px;
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
}

.section-title-icon.blue {
    background: rgba(59, 130, 246, 0.15);
    color: var(--accent-primary);
}

.section-title-icon.cyan {
    background: rgba(34, 211, 238, 0.15);
    color: var(--accent-satellite);
}

.section-title-icon.purple {
    background: rgba(168, 85, 247, 0.15);
    color: var(--accent-compute);
}

.section-link {
    font-size: 0.9rem;
    color: var(--text-secondary);
    display: flex;
    align-items: center;
    gap: var(--space-xs);
}

.section-link:hover {
    color: var(--accent-primary);
}

/* ========================================
   Topic Cards
   ======================================== */
.topics-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: var(--space-xl);
}

.topic-card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-xl);
    padding: var(--space-xl);
    transition: all var(--transition-normal);
}

.topic-card:hover {
    background: var(--bg-card-hover);
    border-color: var(--border-hover);
    transform: translateY(-4px);
}

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

.topic-card-icon {
    width: 48px;
    height: 48px;
    border-radius: var(--radius-lg);
    display: flex;
    align-items: center;
    justify-content: center;
}

.topic-card-icon.satellite {
    background: linear-gradient(135deg, rgba(34, 211, 238, 0.2), rgba(34, 211, 238, 0.05));
    color: var(--accent-satellite);
}

.topic-card-icon.compute {
    background: linear-gradient(135deg, rgba(168, 85, 247, 0.2), rgba(168, 85, 247, 0.05));
    color: var(--accent-compute);
}

.topic-card h3 {
    font-size: 1.25rem;
    font-weight: 700;
}

.topic-card ul {
    list-style: none;
    display: flex;
    flex-direction: column;
    gap: var(--space-sm);
}

.topic-card li {
    color: var(--text-secondary);
    font-size: 0.95rem;
    padding-left: var(--space-lg);
    position: relative;
}

.topic-card li::before {
    content: '';
    position: absolute;
    left: 0;
    top: 0.65em;
    width: 6px;
    height: 6px;
    border-radius: 50%;
}

.topic-card.satellite li::before {
    background: var(--accent-satellite);
}

.topic-card.compute li::before {
    background: var(--accent-compute);
}

/* ========================================
   Article Cards
   ======================================== */
.articles-grid a.article-card,
.articles-grid .article-card {
    display: block;
    text-decoration: none;
    color: inherit;
}
.articles-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: var(--space-lg);
}

.article-card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    overflow: hidden;
    transition: all var(--transition-normal);
}

.article-card:hover {
    background: var(--bg-card-hover);
    border-color: var(--border-hover);
    transform: translateY(-4px);
}

.article-card-image {
    height: 160px;
    background: linear-gradient(135deg, var(--bg-secondary), var(--bg-card));
    display: flex;
    align-items: center;
    justify-content: center;
    position: relative;
}

.article-card-image .category-badge {
    position: absolute;
    top: var(--space-md);
    left: var(--space-md);
    background: rgba(0, 0, 0, 0.6);
    backdrop-filter: blur(8px);
    padding: var(--space-xs) var(--space-sm);
    border-radius: var(--radius-sm);
    font-size: 0.75rem;
    color: var(--text-primary);
}

.article-card-body {
    padding: var(--space-lg);
}

.article-card-meta {
    display: flex;
    align-items: center;
    gap: var(--space-md);
    font-size: 0.8rem;
    color: var(--text-muted);
    margin-bottom: var(--space-sm);
}

.article-card-title {
    font-size: 1.1rem;
    font-weight: 600;
    line-height: 1.4;
    margin-bottom: var(--space-sm);
    color: var(--text-primary);
}

.article-card-title a {
    color: inherit;
}

.article-card-title a:hover {
    color: var(--accent-primary);
}

.article-card-excerpt {
    font-size: 0.9rem;
    color: var(--text-secondary);
    line-height: 1.6;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;
    overflow: hidden;
}

.article-card-footer {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-top: var(--space-md);
    padding-top: var(--space-md);
    border-top: 1px solid var(--border-color);
}

.article-card-date {
    font-size: 0.8rem;
    color: var(--text-muted);
}

.article-card-read {
    font-size: 0.8rem;
    color: var(--text-muted);
}

/* ========================================
   Featured / Large Article Card
   ======================================== */
.article-featured {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-xl);
    overflow: hidden;
    display: grid;
    grid-template-columns: 1fr 1fr;
    transition: all var(--transition-normal);
}

.article-featured:hover {
    border-color: var(--border-hover);
}

.article-featured-image {
    background: linear-gradient(135deg, var(--accent-primary), var(--accent-secondary));
    display: flex;
    align-items: center;
    justify-content: center;
    min-height: 300px;
}

.article-featured-content {
    padding: var(--space-xl);
    display: flex;
    flex-direction: column;
    justify-content: center;
}

.article-featured-label {
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--accent-primary);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-bottom: var(--space-md);
}

.article-featured-title {
    font-size: 1.75rem;
    font-weight: 700;
    line-height: 1.3;
    margin-bottom: var(--space-md);
}

.article-featured-title a {
    color: var(--text-primary);
}

.article-featured-title a:hover {
    color: var(--accent-primary);
}

.article-featured-excerpt {
    font-size: 1rem;
    color: var(--text-secondary);
    line-height: 1.7;
    margin-bottom: var(--space-lg);
}

.article-featured-meta {
    display: flex;
    align-items: center;
    gap: var(--space-lg);
    font-size: 0.875rem;
    color: var(--text-muted);
}

/* ========================================
   Topics Pills
   ======================================== */
.topics-pills {
    display: flex;
    flex-wrap: wrap;
    gap: var(--space-sm);
}

.topic-pill {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: 100px;
    padding: var(--space-sm) var(--space-md);
    font-size: 0.875rem;
    color: var(--text-secondary);
    transition: all var(--transition-fast);
}

.topic-pill:hover {
    background: var(--bg-card-hover);
    border-color: var(--border-hover);
    color: var(--text-primary);
}

.topic-pill.active {
    background: var(--accent-primary);
    border-color: var(--accent-primary);
    color: white;
}

/* ========================================
   Footer
   ======================================== */
.footer {
    background: var(--bg-secondary);
    border-top: 1px solid var(--border-color);
    padding: var(--space-3xl) 0 var(--space-xl);
    margin-top: var(--space-3xl);
}

.footer-grid {
    display: grid;
    grid-template-columns: 2fr 1fr 1fr 1fr;
    gap: var(--space-2xl);
    margin-bottom: var(--space-2xl);
}

.footer-brand h3 {
    font-size: 1.25rem;
    font-weight: 700;
    margin-bottom: var(--space-md);
}

.footer-brand p {
    color: var(--text-secondary);
    font-size: 0.9rem;
    line-height: 1.7;
}

.footer-column h4 {
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--space-md);
}

.footer-column ul {
    list-style: none;
    display: flex;
    flex-direction: column;
    gap: var(--space-sm);
}

.footer-column a {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.footer-column a:hover {
    color: var(--accent-primary);
}

.footer-bottom {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding-top: var(--space-xl);
    border-top: 1px solid var(--border-color);
    color: var(--text-muted);
    font-size: 0.85rem;
}

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

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

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

/* ========================================
   Responsive
   ======================================== */
@media (max-width: 1024px) {
    .topics-grid {
        grid-template-columns: 1fr;
    }
    
    .article-featured {
        grid-template-columns: 1fr;
    }
    
    .article-featured-image {
        min-height: 200px;
    }
    
    .footer-grid {
        grid-template-columns: 1fr 1fr;
    }
}

@media (max-width: 768px) {
    .nav-links {
        display: none;
    }
    
    .hero {
        padding: var(--space-2xl) 0;
    }
    
    .hero h1 {
        font-size: 2rem;
    }
    
    .hero-topics {
        flex-direction: column;
        gap: var(--space-md);
    }
    
    .hero-actions {
        flex-direction: column;
    }
    
    .btn {
        width: 100%;
        justify-content: center;
    }
    
    .section-header {
        flex-direction: column;
        align-items: flex-start;
        gap: var(--space-md);
    }
    
    .articles-grid {
        grid-template-columns: 1fr;
    }
    
    .footer-grid {
        grid-template-columns: 1fr;
    }
    
    .footer-bottom {
        flex-direction: column;
        gap: var(--space-md);
        text-align: center;
    }
}

/* ========================================
   Utilities
   ======================================== */
.sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    border: 0;
}

.text-satellite { color: var(--accent-satellite); }
.text-compute { color: var(--accent-compute); }
.text-primary { color: var(--accent-primary); }