:root {
    /* Professional Dark Theme (default) */
    --color-background: #0d1117;
    --color-surface: #161b22;
    --color-surface-hover: #1c2128;
    --color-border: #30363d;
    --color-border-subtle: #21262d;
    
    --color-text-primary: #e6edf3;
    --color-text-secondary: #8b949e;
    --color-text-muted: #6e7681;
    
    --color-accent: #2f81f7;
    --color-accent-hover: #4493f8;
    --color-accent-subtle: rgba(47, 129, 247, 0.1);
    
    --font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Noto Sans', Helvetica, Arial, sans-serif;
    --font-family-mono: 'SF Mono', Monaco, 'Cascadia Code', 'Roboto Mono', Consolas, 'Courier New', monospace;
    
    --max-width: 1200px;
    --spacing-unit: 8px;
    --border-radius: 6px;
    --border-radius-lg: 12px;
    
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.12);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.15);
    --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.2);
}

/* Professional Light Theme */
[data-theme="light"] {
    --color-background: #ffffff;
    --color-surface: #f6f8fa;
    --color-surface-hover: #eaeef2;
    --color-border: #d0d7de;
    --color-border-subtle: #e5e7eb;
    
    --color-text-primary: #24292f;
    --color-text-secondary: #57606a;
    --color-text-muted: #6e7781;
    
    --color-accent: #0969da;
    --color-accent-hover: #0860ca;
    --color-accent-subtle: rgba(9, 105, 218, 0.08);
    
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.04);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.08);
}

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

body {
    font-family: var(--font-family);
    font-size: 16px;
    line-height: 1.6;
    color: var(--color-text-primary);
    background: var(--color-background);
    margin: 0;
    padding: 0;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

.container {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 0 calc(var(--spacing-unit) * 3);
}

/* Header */
.header {
    background: var(--color-surface);
    border-bottom: 1px solid var(--color-border);
    padding: calc(var(--spacing-unit) * 2) 0;
    position: sticky;
    top: 0;
    z-index: 1000;
    backdrop-filter: blur(8px);
    background: rgba(13, 17, 23, 0.8);
}

[data-theme="light"] .header {
    background: rgba(255, 255, 255, 0.9);
}

.header-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: calc(var(--spacing-unit) * 3);
}

.site-title {
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--color-text-primary);
    text-decoration: none;
    white-space: nowrap;
}

.site-title:hover {
    color: var(--color-accent);
}

/* Navigation */
.nav {
    display: flex;
    align-items: center;
    gap: calc(var(--spacing-unit) * 1);
    flex-wrap: wrap;
}

.nav a {
    color: var(--color-text-secondary);
    text-decoration: none;
    font-size: 0.9375rem;
    padding: calc(var(--spacing-unit) * 1) calc(var(--spacing-unit) * 1.5);
    border-radius: var(--border-radius);
    transition: all 0.2s ease;
    white-space: nowrap;
}

.nav a:hover {
    color: var(--color-text-primary);
    background: var(--color-accent-subtle);
}

.nav a.active {
    color: var(--color-accent);
    background: var(--color-accent-subtle);
    font-weight: 500;
}

/* Dropdown */
.dropdown {
    position: relative;
}

.dropdown-toggle {
    background: none;
    border: none;
    color: var(--color-text-secondary);
    font-family: var(--font-family);
    font-size: 0.9375rem;
    padding: calc(var(--spacing-unit) * 1) calc(var(--spacing-unit) * 1.5);
    border-radius: var(--border-radius);
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 6px;
    transition: all 0.2s ease;
    white-space: nowrap;
}

.dropdown-toggle:hover {
    color: var(--color-text-primary);
    background: var(--color-accent-subtle);
}

.dropdown-toggle svg {
    width: 14px;
    height: 14px;
    fill: currentColor;
    transition: transform 0.2s ease;
}

.dropdown-toggle.active svg {
    transform: rotate(180deg);
}

.dropdown-menu {
    position: absolute;
    top: calc(100% + 4px);
    right: 0;
    min-width: 200px;
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--border-radius);
    box-shadow: var(--shadow-lg);
    opacity: 0;
    visibility: hidden;
    transform: translateY(-8px);
    transition: all 0.2s ease;
    z-index: 1000;
}

.dropdown-menu.show {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

.dropdown-menu a {
    display: block;
    padding: calc(var(--spacing-unit) * 1.5) calc(var(--spacing-unit) * 2);
    color: var(--color-text-secondary);
    text-decoration: none;
    font-size: 0.9375rem;
    border-bottom: 1px solid var(--color-border-subtle);
    transition: all 0.15s ease;
}

.dropdown-menu a:last-child {
    border-bottom: none;
}

.dropdown-menu a:hover {
    background: var(--color-surface-hover);
    color: var(--color-text-primary);
}

.dropdown-menu a.active {
    color: var(--color-accent);
    font-weight: 500;
}

/* Theme Toggle */
.theme-toggle {
    background: var(--color-surface-hover);
    border: 1px solid var(--color-border);
    color: var(--color-text-secondary);
    padding: calc(var(--spacing-unit) * 1) calc(var(--spacing-unit) * 1.5);
    border-radius: var(--border-radius);
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 6px;
    transition: all 0.2s ease;
    margin-left: calc(var(--spacing-unit) * 1);
}

.theme-toggle:hover {
    border-color: var(--color-accent);
    background: var(--color-accent-subtle);
    color: var(--color-accent);
}

.theme-toggle svg {
    width: 16px;
    height: 16px;
    fill: currentColor;
}

/* Main Content */
.main {
    padding: calc(var(--spacing-unit) * 6) 0;
    min-height: calc(100vh - 300px);
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
    color: var(--color-text-primary);
    font-weight: 600;
    line-height: 1.25;
    margin-bottom: calc(var(--spacing-unit) * 2);
}

h1 {
    font-size: 2.5rem;
    font-weight: 700;
    margin-bottom: calc(var(--spacing-unit) * 3);
}

h2 {
    font-size: 2rem;
    margin-top: calc(var(--spacing-unit) * 6);
    margin-bottom: calc(var(--spacing-unit) * 2);
    padding-bottom: calc(var(--spacing-unit) * 2);
    border-bottom: 1px solid var(--color-border);
    position: relative;
    cursor: pointer;
    user-select: none;
}

h2:hover {
    color: var(--color-accent);
}

h2::before {
    content: '▼';
    position: absolute;
    left: -24px;
    color: var(--color-accent);
    font-size: 0.75em;
    transition: transform 0.2s ease;
}

h2.collapsed::before {
    transform: rotate(-90deg);
}

h3 {
    font-size: 1.5rem;
    margin-top: calc(var(--spacing-unit) * 4);
}

h4 {
    font-size: 1.25rem;
    margin-top: calc(var(--spacing-unit) * 3);
}

p {
    margin-bottom: calc(var(--spacing-unit) * 2);
    color: var(--color-text-secondary);
    line-height: 1.7;
}

/* Links */
a {
    color: var(--color-accent);
    text-decoration: none;
}

a:hover {
    text-decoration: underline;
}

/* Lists */
ul, ol {
    margin-bottom: calc(var(--spacing-unit) * 2);
    padding-left: calc(var(--spacing-unit) * 4);
}

li {
    margin-bottom: calc(var(--spacing-unit) * 1);
    color: var(--color-text-secondary);
}

/* Code */
code {
    font-family: var(--font-family-mono);
    font-size: 0.875em;
    background: var(--color-accent-subtle);
    color: var(--color-accent);
    padding: 2px 6px;
    border-radius: 3px;
    border: 1px solid var(--color-border-subtle);
}

pre {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--border-radius);
    padding: calc(var(--spacing-unit) * 2);
    overflow-x: auto;
    margin: calc(var(--spacing-unit) * 3) 0;
}

pre code {
    background: none;
    border: none;
    padding: 0;
    color: var(--color-text-primary);
}

/* Blockquotes */
blockquote {
    border-left: 3px solid var(--color-accent);
    padding: calc(var(--spacing-unit) * 2) calc(var(--spacing-unit) * 3);
    margin: calc(var(--spacing-unit) * 3) 0;
    background: var(--color-surface);
    border-radius: 0 var(--border-radius) var(--border-radius) 0;
    color: var(--color-text-secondary);
}

blockquote p:last-child {
    margin-bottom: 0;
}

/* Tables */
table {
    width: 100%;
    border-collapse: collapse;
    margin: calc(var(--spacing-unit) * 3) 0;
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--border-radius);
    overflow: hidden;
}

th, td {
    padding: calc(var(--spacing-unit) * 1.5);
    text-align: left;
    border-bottom: 1px solid var(--color-border);
}

th {
    background: var(--color-surface-hover);
    font-weight: 600;
    color: var(--color-text-primary);
}

tr:last-child td {
    border-bottom: none;
}

tr:hover {
    background: var(--color-surface-hover);
}

/* Hero Section */
.hero {
    text-align: center;
    padding: calc(var(--spacing-unit) * 8) calc(var(--spacing-unit) * 3);
    margin-bottom: calc(var(--spacing-unit) * 6);
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--border-radius-lg);
}

.hero h1 {
    font-size: 3rem;
    margin-bottom: calc(var(--spacing-unit) * 2);
}

.hero p {
    font-size: 1.25rem;
    color: var(--color-text-secondary);
    max-width: 700px;
    margin: 0 auto;
}

/* Methodology Section */
.methodology-section {
    margin: calc(var(--spacing-unit) * 6) 0;
}

.methodology-content {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--border-radius-lg);
    padding: calc(var(--spacing-unit) * 4);
    transition: all 0.2s ease;
}

.methodology-content:hover {
    border-color: var(--color-accent);
    box-shadow: var(--shadow-md);
}

.methodology-link {
    text-decoration: none;
    color: inherit;
}

.methodology-content h2 {
    margin-top: 0;
    border-bottom: none;
    padding-bottom: 0;
    margin-bottom: calc(var(--spacing-unit) * 2);
}

.methodology-content p {
    margin-bottom: 0;
}

/* Domains Section */
.domains-section {
    margin: calc(var(--spacing-unit) * 6) 0;
}

.domains-section h2 {
    margin-top: 0;
    margin-bottom: calc(var(--spacing-unit) * 4);
}

.domain-links {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: calc(var(--spacing-unit) * 3);
}

.domain-link {
    text-decoration: none;
    color: inherit;
}

.domain-content {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--border-radius-lg);
    padding: calc(var(--spacing-unit) * 3);
    height: 100%;
    transition: all 0.2s ease;
}

.domain-content:hover {
    border-color: var(--color-accent);
    box-shadow: var(--shadow-md);
    transform: translateY(-2px);
}

.domain-content h3 {
    margin-top: 0;
    margin-bottom: calc(var(--spacing-unit) * 1.5);
    color: var(--color-text-primary);
}

.domain-content p {
    margin-bottom: 0;
    font-size: 0.9375rem;
}

/* Back Link */
.back-link {
    display: inline-flex;
    align-items: center;
    margin-bottom: calc(var(--spacing-unit) * 3);
    color: var(--color-accent);
    text-decoration: none;
    font-size: 0.9375rem;
    padding: calc(var(--spacing-unit) * 1) calc(var(--spacing-unit) * 2);
    background: var(--color-accent-subtle);
    border: 1px solid var(--color-border);
    border-radius: var(--border-radius);
    transition: all 0.2s ease;
}

.back-link:hover {
    background: var(--color-surface-hover);
    border-color: var(--color-accent);
    text-decoration: none;
}

.back-link::before {
    content: "←";
    margin-right: calc(var(--spacing-unit) * 1);
}

/* Footer */
.footer {
    background: var(--color-surface);
    border-top: 1px solid var(--color-border);
    padding: calc(var(--spacing-unit) * 4) 0;
    margin-top: calc(var(--spacing-unit) * 8);
    text-align: center;
    color: var(--color-text-secondary);
}

.footer p {
    margin: 0;
    font-size: 0.9375rem;
}

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

/* Responsive Design */
@media (max-width: 768px) {
    .header-content {
        flex-direction: column;
        gap: calc(var(--spacing-unit) * 2);
        align-items: stretch;
    }
    
    .nav {
        flex-direction: column;
        gap: calc(var(--spacing-unit) * 1);
        width: 100%;
    }
    
    .nav a,
    .dropdown-toggle,
    .theme-toggle {
        width: 100%;
        justify-content: center;
    }
    
    .dropdown-menu {
        position: static;
        transform: none;
        box-shadow: none;
        border: none;
        border-top: 1px solid var(--color-border);
        border-radius: 0;
        margin-top: calc(var(--spacing-unit) * 1);
    }
    
    .domain-links {
        grid-template-columns: 1fr;
        gap: calc(var(--spacing-unit) * 2);
    }
    
    .hero h1 {
        font-size: 2rem;
    }
    
    .hero p {
        font-size: 1.125rem;
    }
    
    h1 {
        font-size: 2rem;
    }
    
    h2 {
        font-size: 1.5rem;
    }
    
    h3 {
        font-size: 1.25rem;
    }
    
    .container {
        padding: 0 calc(var(--spacing-unit) * 2);
    }
}

@media (max-width: 480px) {
    .hero {
        padding: calc(var(--spacing-unit) * 4) calc(var(--spacing-unit) * 2);
    }
    
    .methodology-content,
    .domain-content {
        padding: calc(var(--spacing-unit) * 2.5);
    }
}

/* Collapsible Sections */
.section-content {
    max-height: 5000px;
    overflow: hidden;
    transition: max-height 0.3s ease, opacity 0.3s ease;
    opacity: 1;
}

.section-content.collapsed {
    max-height: 0;
    opacity: 0;
    margin: 0;
    padding: 0;
}

.collapsible-anchor {
    position: relative;
    display: block;
}

/* Smooth scroll with offset for sticky header */
html {
    scroll-padding-top: 80px;
}

/* Print Styles */
@media print {
    .header,
    .footer,
    .theme-toggle,
    .back-link {
        display: none;
    }
    
    body {
        background: white;
        color: black;
    }
    
    .main {
        padding: 0;
    }
    
    /* Show all sections when printing */
    h2::before {
        display: none;
    }
    
    .section-content {
        max-height: none !important;
        opacity: 1 !important;
    }
}

.section-link:nth-child(8) { animation-delay: 0.8s; }