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

:root {
    --primary-color: #0ea5e9;      /* Sky blue*/
    --primary-dark: #0284c7;       /* Deeper blue */
    --primary-light: #7dd3fc;      /* Light blue */
    --secondary-color: #8b5cf6;    /* Purple */
    --accent-color: #f59e0b;       /* Amber */
    --accent-secondary: #10b981;   /* Emerald */
    
    /* Neutral Colors - More Refined */
    --text-color: #f8fafc;         /* Bright white */
    --text-light: #cbd5e1;         /* Softer light gray */
    --text-muted: #94a3b8;         /* Muted gray */
    
    /* Background Colors - Deeper and Richer */
    --bg-color: #0f172a;           /* Deep navy */
    --bg-secondary: #1e293b;       /* Dark slate */
    --card-bg: #1e293b;            /* Card background */
    --card-hover: #334155;         /* Card hover state */
    
    /* Sidebar Colors */
    --sidebar-bg: #0f172a;         /* Deep navy */
    --sidebar-text: #f1f5f9;       /* Soft white */
    --sidebar-border: #334155;     /* Border color */
    
    /* UI Colors */
    --shadow: 0 4px 12px rgba(0, 0, 0, 0.4);
    --shadow-hover: 0 8px 25px rgba(0, 0, 0, 0.5);
    --border-radius: 12px;
    --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
    overflow-x: hidden;
    font-size: 16px;
}

.container {
    display: flex;
    min-height: 100vh;
    flex-direction: column;
}

/* Sidebar Styles */
.sidebar {
    width: 100%;
    background: var(--sidebar-bg);
    color: var(--sidebar-text);
    padding: 1rem 0;
    position: fixed;
    height: auto;
    transition: var(--transition);
    z-index: 1000;
    border-right: 1px solid var(--sidebar-border);
    transform: translateY(-100%);
    top: 0;
    left: 0;
    right: 0;
    max-height: 80vh;
    overflow-y: auto;
}

.sidebar.active {
    transform: translateY(0);
}

.sidebar-header {
    padding: 0 1.25rem 1.25rem;
    border-bottom: 1px solid var(--sidebar-border);
    margin-bottom: 1.25rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    position: sticky;
    top: 0;
    background: var(--sidebar-bg);
    z-index: 10;
}

.sidebar-title {
    font-size: 1.3rem;
    display: flex;
    align-items: center;
    gap: 0.625rem;
    color: var(--primary-color);
    font-weight: 600;
}

.sidebar-toggle {
    display: block;
    background: none;
    border: none;
    color: var(--sidebar-text);
    font-size: 1.2rem;
    cursor: pointer;
    padding: 0.5rem;
    border-radius: 6px;
    transition: var(--transition);
}

.sidebar-toggle:hover {
    background: rgba(255, 255, 255, 0.1);
}

.sidebar-nav {
    list-style: none;
    margin-bottom: 1.25rem;
}

.nav-item {
    margin: 0.25rem 0;
}

.nav-link {
    display: flex;
    align-items: center;
    gap: 0.9375rem;
    padding: 1rem 1.25rem;
    color: var(--sidebar-text);
    text-decoration: none;
    transition: var(--transition);
    border-left: 3px solid transparent;
    font-size: 0.95rem;
    border-radius: 0 8px 8px 0;
}

.nav-link:hover {
    background: linear-gradient(90deg, rgba(14, 165, 233, 0.1), transparent);
    border-left-color: var(--primary-color);
    color: var(--primary-light);
}

.nav-link.active {
    background: linear-gradient(90deg, rgba(14, 165, 233, 0.15), transparent);
    border-left-color: var(--primary-color);
    color: var(--primary-color);
    font-weight: 500;
}

.nav-link i {
    width: 1.25rem;
    text-align: center;
    font-size: 1rem;
}

.sidebar-footer {
    padding: 1.25rem;
    border-top: 1px solid var(--sidebar-border);
    margin-top: auto;
    position: sticky;
    bottom: 0;
    background: var(--sidebar-bg);
}

.progress-stats {
    display: flex;
    flex-direction: column;
    gap: 0.9375rem;
}

.progress-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    font-size: 0.9rem;
}

.progress-item span {
    color: var(--text-muted);
}

.progress-item strong {
    color: var(--primary-color);
    font-weight: 600;
}

/* Social Links Styles */
.social-links {
    display: flex;
    gap: 1rem;
    margin-top: 1.5rem;
    justify-content: center;
    flex-wrap: wrap;
}

.social-link {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    padding: 1rem 1.5rem;
    background: linear-gradient(135deg, var(--card-bg), var(--bg-secondary));
    color: var(--text-color);
    text-decoration: none;
    border-radius: 10px;
    border: 1px solid var(--sidebar-border);
    transition: var(--transition);
    font-size: 0.95rem;
    font-weight: 500;
    box-shadow: var(--shadow);
}

.social-link:hover {
    transform: translateY(-3px);
    border-color: var(--primary-color);
    box-shadow: var(--shadow-hover);
}

.social-link.github {
    background: linear-gradient(135deg, #1a1a1a, #2d2d2d);
    border-color: #404040;
}

.social-link.github:hover {
    background: linear-gradient(135deg, #2d2d2d, #404040);
    border-color: var(--primary-color);
}

.social-link.twitter {
    background: linear-gradient(135deg, #0f1419, #1e2732);
    border-color: #334155;
}

.social-link.twitter:hover {
    background: linear-gradient(135deg, #1e2732, #2d3748);
    border-color: var(--primary-color);
}

.social-link i {
    font-size: 1.2rem;
}

/* Sidebar Social Links */
.sidebar-social {
    padding: 1rem 1.25rem;
    border-top: 1px solid var(--sidebar-border);
}

.sidebar-social-links {
    display: flex;
    gap: 0.75rem;
}

.sidebar-social-link {
    flex: 1;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    padding: 0.75rem;
    background: var(--bg-secondary);
    color: var(--text-color);
    text-decoration: none;
    border-radius: 8px;
    border: 1px solid var(--sidebar-border);
    transition: var(--transition);
    font-size: 0.85rem;
    text-align: center;
}

.sidebar-social-link:hover {
    background: var(--card-hover);
    border-color: var(--primary-color);
    transform: translateY(-1px);
}

.sidebar-social-link.github:hover {
    background: #2d2d2d;
    border-color: var(--primary-color);
}

.sidebar-social-link.twitter:hover {
    background: #1e2732;
    border-color: var(--primary-color);
}

/* Main Content Styles */
.main-content {
    flex: 1;
    padding: 0;
    transition: var(--transition);
    margin-top: 0;
}

.content-section {
    padding: 1.25rem;
    min-height: 100vh;
}

/* Home Section Styles */
.hero-header {
    text-align: center;
    padding: 3rem 1.25rem;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    border-radius: var(--border-radius);
    margin-bottom: 2rem;
    position: relative;
    overflow: hidden;
    box-shadow: var(--shadow);
}

.hero-header::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: linear-gradient(45deg, rgba(0,0,0,0.3), rgba(0,0,0,0.1));
}

.hero-title {
    font-size: 2rem;
    margin-bottom: 1rem;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 1rem;
    position: relative;
    flex-wrap: wrap;
    font-weight: 700;
    text-shadow: 0 2px 4px rgba(0,0,0,0.3);
}

.hero-title i {
    font-size: 2.5rem;
    filter: drop-shadow(0 2px 4px rgba(0,0,0,0.3));
}

.hero-subtitle {
    font-size: 1.1rem;
    opacity: 0.95;
    margin-bottom: 2rem;
    position: relative;
    line-height: 1.5;
    font-weight: 300;
    text-shadow: 0 1px 2px rgba(0,0,0,0.3);
}

.welcome-message {
    background: var(--card-bg);
    padding: 2rem;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    margin-bottom: 2rem;
    text-align: center;
    border: 1px solid var(--sidebar-border);
    position: relative;
    overflow: hidden;
}

.welcome-message h2 {
    color: var(--primary-color);
    margin-bottom: 1.5rem;
    font-size: 1.8rem;
    font-weight: 600;
}

.welcome-message p {
    font-size: 1.05rem;
    line-height: 1.7;
    color: var(--text-light);
    max-width: 100%;
    margin: 0 auto 1.5rem;
}

.quick-links {
    margin-bottom: 2rem;
}

.quick-links h3 {
    margin-bottom: 1.5rem;
    color: var(--text-color);
    font-size: 1.5rem;
    font-weight: 600;
    text-align: center;
}

.link-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 1.5rem;
}

.quick-link {
    background: var(--card-bg);
    padding: 2rem 1.5rem;
    border-radius: var(--border-radius);
    text-decoration: none;
    color: var(--text-color);
    text-align: center;
    box-shadow: var(--shadow);
    transition: var(--transition);
    border: 1px solid var(--sidebar-border);
    display: block;
    min-height: 160px;
    display: flex;
    flex-direction: column;
    justify-content: center;
    position: relative;
    overflow: hidden;
}

.quick-link::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 3px;
    background: linear-gradient(90deg, var(--primary-color), var(--accent-secondary));
    transform: scaleX(0);
    transition: var(--transition);
}

.quick-link:hover {
    transform: translateY(-5px);
    border-color: var(--primary-color);
    box-shadow: var(--shadow-hover);
    background: var(--card-hover);
}

.quick-link:hover::before {
    transform: scaleX(1);
}

.quick-link i {
    font-size: 2.5rem;
    color: var(--primary-color);
    margin-bottom: 1rem;
    display: block;
    transition: var(--transition);
}

.quick-link:hover i {
    color: var(--accent-color);
    transform: scale(1.1);
}

.quick-link span {
    font-weight: 600;
    font-size: 1.2rem;
    display: block;
    margin-bottom: 0.75rem;
    line-height: 1.3;
    color: var(--text-color);
}

.quick-link p {
    color: var(--text-muted);
    font-size: 0.95rem;
    line-height: 1.5;
}

/* Section Content Styles */
.section-header {
    display: flex;
    align-items: center;
    gap: 1.5rem;
    margin-bottom: 2rem;
    padding: 2rem;
    background: var(--card-bg);
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    border: 1px solid var(--sidebar-border);
    flex-direction: column;
    text-align: center;
    position: relative;
    overflow: hidden;
}

.section-header::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 3px;
    background: linear-gradient(90deg, var(--primary-color), var(--secondary-color));
}

.section-icon {
    font-size: 3rem;
    color: var(--primary-color);
    filter: drop-shadow(0 2px 4px rgba(0,0,0,0.2));
}

.section-header h1 {
    color: var(--text-color);
    font-size: 1.8rem;
    margin-bottom: 0.75rem;
    line-height: 1.3;
    font-weight: 600;
}

.section-header p {
    color: var(--text-muted);
    font-size: 1.1rem;
    line-height: 1.5;
    max-width: 600px;
}

.topics-container {
    display: grid;
    gap: 1.5rem;
}

.topic-category {
    background: var(--card-bg);
    border-radius: var(--border-radius);
    padding: 2rem;
    box-shadow: var(--shadow);
    border-left: 4px solid var(--primary-color);
    border: 1px solid var(--sidebar-border);
    position: relative;
    overflow: hidden;
}

.topic-category::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 2px;
    background: linear-gradient(90deg, var(--primary-color), transparent);
}

.topic-category h3 {
    color: var(--text-color);
    margin-bottom: 1.5rem;
    font-size: 1.3rem;
    display: flex;
    align-items: center;
    gap: 0.75rem;
    line-height: 1.3;
    font-weight: 600;
}

.topic-category h3 i {
    color: var(--primary-color);
    font-size: 1.2rem;
}

.topic-list {
    list-style: none;
    display: grid;
    gap: 1rem;
}

.topic-item {
    padding: 1.25rem;
    background: var(--bg-secondary);
    border-radius: 8px;
    transition: var(--transition);
    border-left: 3px solid transparent;
    border: 1px solid var(--sidebar-border);
    position: relative;
}

.topic-item:hover {
    background: var(--card-hover);
    border-left-color: var(--primary-color);
    transform: translateX(5px);
    box-shadow: 0 4px 12px rgba(0,0,0,0.2);
}

.topic-item strong {
    color: var(--text-color);
    display: block;
    margin-bottom: 0.75rem;
    font-size: 1.05rem;
    line-height: 1.3;
    font-weight: 600;
}

.topic-item .subtopics {
    margin-left: 0;
    margin-top: 0.75rem;
}

.subtopic {
    padding: 0.75rem 0;
    color: var(--text-light);
    font-size: 0.95rem;
    border-bottom: 1px solid var(--sidebar-border);
    line-height: 1.5;
    transition: var(--transition);
}

.subtopic:hover {
    color: var(--text-color);
    background: rgba(255,255,255,0.02);
    padding-left: 0.5rem;
}

.subtopic:last-child {
    border-bottom: none;
}

/* Link styles for subtopics */
.subtopic-link {
    color: var(--primary-light);
    text-decoration: none;
    transition: var(--transition);
    border-bottom: 1px dotted var(--primary-light);
    display: inline-block;
    padding: 0.125rem 0;
    line-height: 1.4;
    font-weight: 500;
}

.subtopic-link:hover {
    color: var(--accent-color);
    border-bottom-color: var(--accent-color);
    transform: translateX(2px);
}

.subtopic-link i {
    margin-left: 0.25rem;
    font-size: 0.7rem;
    transition: var(--transition);
}

.subtopic-link:hover i {
    transform: translateX(2px);
}

/* Article Content Styles */
.article-content {
    max-width: 100%;
    margin: 0 auto;
}

.article-section {
    margin-bottom: 2rem;
    padding: 2rem;
    background: var(--card-bg);
    border-radius: var(--border-radius);
    border: 1px solid var(--sidebar-border);
    position: relative;
    overflow: hidden;
}

.article-section::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 2px;
    background: linear-gradient(90deg, var(--primary-color), var(--accent-secondary));
}

.article-section h2 {
    color: var(--primary-color);
    margin-bottom: 1.5rem;
    font-size: 1.6rem;
    border-bottom: 2px solid var(--primary-color);
    padding-bottom: 0.75rem;
    line-height: 1.3;
    font-weight: 600;
}

.article-section h3 {
    color: var(--text-color);
    margin-bottom: 1.25rem;
    font-size: 1.3rem;
    line-height: 1.3;
    font-weight: 600;
}

.article-section h4 {
    color: var(--primary-color);
    margin-bottom: 1rem;
    font-size: 1.1rem;
    line-height: 1.3;
    font-weight: 600;
}

.article-section p {
    margin-bottom: 1.25rem;
    line-height: 1.7;
    color: var(--text-light);
    font-size: 1rem;
}

.article-section em {
    color: var(--accent-color);
    font-style: italic;
    font-weight: 500;
}

.article-section strong {
    color: var(--text-color);
    font-weight: 600;
}

/* Comparison Grid */
.comparison-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: 1.5rem;
    margin: 1.5rem 0;
}

.comparison-item {
    background: var(--bg-secondary);
    padding: 1.5rem;
    border-radius: 8px;
    border-left: 4px solid var(--primary-color);
    border: 1px solid var(--sidebar-border);
    position: relative;
}

.comparison-item::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 2px;
    background: linear-gradient(90deg, var(--primary-color), transparent);
}

.comparison-item h4 {
    margin-bottom: 1.25rem;
    color: var(--primary-color);
    font-size: 1.1rem;
}

.comparison-item ul {
    list-style: none;
    padding-left: 0;
}

.comparison-item li {
    padding: 0.75rem 0;
    border-bottom: 1px solid var(--sidebar-border);
    color: var(--text-light);
    font-size: 0.95rem;
    line-height: 1.5;
    position: relative;
    padding-left: 1.5rem;
}

.comparison-item li::before {
    content: '•';
    color: var(--primary-color);
    position: absolute;
    left: 0;
    font-weight: bold;
}

.comparison-item li:last-child {
    border-bottom: none;
}

/* Related Concepts */
.related-concepts {
    display: flex;
    flex-wrap: wrap;
    gap: 0.75rem;
    margin-top: 1.25rem;
}

.concept-link {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    padding: 0.75rem 1.25rem;
    border-radius: 20px;
    text-decoration: none;
    font-size: 0.9rem;
    border: 1px solid transparent;
    transition: var(--transition);
    line-height: 1.2;
    font-weight: 500;
    box-shadow: 0 2px 8px rgba(14, 165, 233, 0.3);
}

.concept-link:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 15px rgba(14, 165, 233, 0.4);
    background: linear-gradient(135deg, var(--primary-dark), var(--secondary-color));
}

/* Citation */
.citation {
    background: linear-gradient(135deg, var(--bg-secondary), var(--card-bg));
    border-left-color: var(--secondary-color);
}

.citation h3 {
    color: var(--secondary-color);
}

/* Mobile-First Responsive Design */
@media (max-width: 480px) {
    .content-section {
        padding: 1rem;
    }
    
    .hero-title {
        font-size: 1.75rem;
        gap: 0.5rem;
    }
    
    .hero-title i {
        font-size: 2rem;
    }
    
    .hero-subtitle {
        font-size: 1rem;
    }
    
    .section-header {
        padding: 1.5rem;
        gap: 1rem;
    }
    
    .section-header h1 {
        font-size: 1.5rem;
    }
    
    .topic-category {
        padding: 1.5rem;
    }
    
    .article-section {
        padding: 1.5rem;
    }
    
    .article-section h2 {
        font-size: 1.4rem;
    }
    
    .quick-link {
        min-height: 140px;
        padding: 1.5rem 1rem;
    }
    
    .quick-link i {
        font-size: 2rem;
    }
    
    .link-grid {
        grid-template-columns: 1fr;
    }
}

@media (min-width: 481px) and (max-width: 768px) {
    .content-section {
        padding: 1.5rem;
    }
    
    .hero-title {
        font-size: 2.25rem;
    }
    
    .link-grid {
        grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    }
    
    .comparison-grid {
        grid-template-columns: 1fr 1fr;
    }
}

@media (min-width: 769px) {
    .container {
        flex-direction: row;
    }
    
    .sidebar {
        width: 300px;
        height: 100vh;
        position: fixed;
        transform: translateX(0);
        top: 0;
        left: 0;
        max-height: none;
    }
    
    .sidebar-toggle {
        display: none;
    }
    
    .main-content {
        margin-left: 300px;
    }
    
    .content-section {
        padding: 2.5rem;
    }
    
    .section-header {
        flex-direction: row;
        text-align: left;
        padding: 2.5rem;
    }
    
    .section-header h1 {
        font-size: 2.2rem;
    }
    
    .article-content {
        max-width: 800px;
    }
    
    .comparison-grid {
        grid-template-columns: 1fr 1fr;
    }
    
    .topic-item .subtopics {
        margin-left: 0.625rem;
    }
}

/* Touch Device Optimizations */
@media (hover: none) and (pointer: coarse) {
    .quick-link:hover {
        transform: none;
    }
    
    .topic-item:hover {
        transform: none;
        background: var(--card-hover);
    }
    
    .nav-link:hover {
        background: transparent;
    }
    
    /* Add touch-friendly tap targets */
    .nav-link,
    .quick-link,
    .subtopic-link,
    .concept-link,
    .social-link {
        min-height: 44px;
    }
    
    .sidebar-toggle {
        min-width: 44px;
        min-height: 44px;
    }
}

/* Reduced Motion Support */
@media (prefers-reduced-motion: reduce) {
    * {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}

/* High Contrast Support */
@media (prefers-contrast: high) {
    :root {
        --text-color: #ffffff;
        --text-light: #e2e8f0;
        --text-muted: #cbd5e1;
        --card-bg: #000000;
        --sidebar-bg: #000000;
        --sidebar-border: #4a5568;
    }
    
    .topic-item,
    .article-section,
    .comparison-item {
        border: 2px solid var(--primary-color);
    }
}

/* Scrollbar Styling */
::-webkit-scrollbar {
    width: 8px;
}

::-webkit-scrollbar-track {
    background: var(--bg-secondary);
    border-radius: 4px;
}

::-webkit-scrollbar-thumb {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: linear-gradient(135deg, var(--primary-dark), var(--secondary-color));
}

/* Animation for content */
@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.fade-in {
    animation: fadeInUp 0.5s cubic-bezier(0.4, 0, 0.2, 1);
}

/* Focus styles for accessibility */
button:focus-visible,
a:focus-visible {
    outline: 2px solid var(--accent-color);
    outline-offset: 2px;
    border-radius: 4px;
}

/* Loading state */
.loading {
    opacity: 0.7;
    pointer-events: none;
}

/* Print styles */
@media print {
    .sidebar,
    .sidebar-toggle,
    .social-links {
        display: none;
    }
    
    .main-content {
        margin-left: 0;
    }
    
    .quick-link:hover {
        transform: none;
    }
    
    .hero-header {
        background: #000 !important;
        color: #000 !important;
    }
    
    body {
        background: white !important;
        color: black !important;
    }
}

/* Papers Index Styles */
.papers-index {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 2rem;
    margin-top: 1rem;
}

.index-column h4 {
    color: var(--primary-color);
    margin-bottom: 1rem;
    font-size: 1.1rem;
    font-weight: 600;
    border-bottom: 2px solid var(--primary-color);
    padding-bottom: 0.5rem;
}

.index-list {
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
}

.index-item {
    display: flex;
    flex-direction: column;
    padding: 1rem;
    background: var(--bg-secondary);
    border-radius: 8px;
    text-decoration: none;
    color: var(--text-color);
    border: 1px solid var(--sidebar-border);
    transition: var(--transition);
    position: relative;
    overflow: hidden;
}

.index-item::before {
    content: '';
    position: absolute;
    left: 0;
    top: 0;
    bottom: 0;
    width: 3px;
    background: linear-gradient(to bottom, var(--primary-color), var(--secondary-color));
    transform: scaleY(0);
    transition: var(--transition);
}

.index-item:hover {
    background: var(--card-hover);
    transform: translateX(5px);
    border-color: var(--primary-color);
}

.index-item:hover::before {
    transform: scaleY(1);
}

.index-title {
    font-weight: 600;
    font-size: 1rem;
    margin-bottom: 0.25rem;
    line-height: 1.3;
}

.index-meta {
    color: var(--text-muted);
    font-size: 0.85rem;
    line-height: 1.4;
}

@media (max-width: 480px) {
    .index-item {
        padding: 0.75rem;
    }
    
    .category-item {
        padding: 0.5rem 0.75rem;
    }
}

/* Series Intro Styles */
.series-intro {
    max-width: 800px;
    margin: 0 auto;
}

.series-description {
    background: var(--card-bg);
    border-radius: 12px;
    padding: 2rem;
    margin-bottom: 2rem;
    border-left: 4px solid var(--primary-color);
}

.series-description p {
    font-size: 1.1rem;
    line-height: 1.6;
    color: var(--text-color);
    margin: 0;
}

.series-parts {
    margin-bottom: 3rem;
}

.series-parts h3 {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    margin-bottom: 1.5rem;
    color: var(--primary-color);
}

.series-part-card {
    display: flex;
    background: var(--card-bg);
    border-radius: 12px;
    padding: 1.5rem;
    margin-bottom: 1rem;
    transition: all 0.3s ease;
    border: 1px solid var(--border-color);
}

.series-part-card:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 25px rgba(0,0,0,0.1);
    border-color: var(--primary-color);
}

.part-number {
    background: var(--primary-color);
    color: white;
    border-radius: 8px;
    padding: 0.5rem 1rem;
    font-weight: bold;
    margin-right: 1.5rem;
    align-self: flex-start;
    min-width: 70px;
    text-align: center;
}

.part-content {
    flex: 1;
}

.part-content h4 {
    margin: 0 0 0.5rem 0;
    font-size: 1.2rem;
}

.part-link {
    color: var(--text-color);
    text-decoration: none;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

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

.part-content p {
    margin: 0;
    color: var(--text-muted);
    line-height: 1.5;
}

.series-navigation {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 1rem;
    padding-top: 2rem;
    border-top: 1px solid var(--border-color);
}

.btn {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.75rem 1.5rem;
    border-radius: 8px;
    text-decoration: none;
    font-weight: 600;
    transition: all 0.3s ease;
    border: none;
    cursor: pointer;
}

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

.btn-primary:hover {
    background: var(--primary-dark);
    transform: translateY(-2px);
}

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

.btn-secondary:hover {
    background: var(--border-color);
    transform: translateY(-2px);
}

/* Coming Soon Styles */
.subtopic-link.coming-soon {
    color: var(--text-muted);
    cursor: not-allowed;
}

.subtopic-link.coming-soon:hover {
    color: var(--text-muted);
}