:root {
    --primary-color: #2563eb;
    --primary-dark: #1d4ed8;
    --text-color: #1f2937;
    --text-muted: #6b7280;
    --bg-color: #ffffff;
    --code-bg: #f3f4f6;
    --border-color: #e5e7eb;
    --max-width: 900px;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, sans-serif;
    line-height: 1.7;
    color: var(--text-color);
    background-color: var(--bg-color);
}

/* Header and Navigation */
header {
    background: var(--primary-color);
    color: white;
    padding: 1rem 2rem;
    position: sticky;
    top: 0;
    z-index: 100;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

header nav {
    max-width: var(--max-width);
    margin: 0 auto;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

header .logo {
    font-weight: bold;
    font-size: 1.25rem;
    color: white;
    text-decoration: none;
}

header .nav-links {
    display: flex;
    align-items: center;
    gap: 0.25rem;
}

header .nav-links a {
    color: white;
    text-decoration: none;
    padding: 0.5rem;
    border-radius: 4px;
    transition: background 0.2s, opacity 0.2s;
    display: flex;
    align-items: center;
    justify-content: center;
    opacity: 0.85;
}

header .nav-links a:hover {
    background: rgba(255, 255, 255, 0.15);
    opacity: 1;
}

header .nav-links svg {
    display: block;
}

/* Layout with Sidebar */
.layout {
    display: flex;
    max-width: 1400px;
    margin: 0 auto;
}

/* Sidebar */
.sidebar {
    width: 280px;
    flex-shrink: 0;
    position: sticky;
    top: 60px; /* Below header */
    height: calc(100vh - 60px);
    overflow-y: auto;
    border-right: 1px solid var(--border-color);
    background: var(--bg-color);
}

#TOC {
    padding: 1.5rem;
}

#TOC h2 {
    font-size: 0.875rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-muted);
    margin-bottom: 1rem;
    padding-bottom: 0.5rem;
    border-bottom: 1px solid var(--border-color);
}

#TOC > ul {
    margin: 0;
}

#TOC ul {
    list-style: none;
    padding-left: 0;
}

#TOC > ul > li > ul {
    padding-left: 0.75rem;
    margin-top: 0.25rem;
}

#TOC > ul > li > ul > li > ul {
    padding-left: 0.75rem;
}

#TOC li {
    margin: 0.2rem 0;
}

#TOC > ul > li {
    margin: 0.5rem 0;
}

#TOC a {
    color: var(--text-color);
    text-decoration: none;
    font-size: 0.9rem;
    display: block;
    padding: 0.2rem 0;
    transition: color 0.15s;
}

#TOC > ul > li > a {
    font-weight: 500;
    color: var(--text-color);
}

#TOC a:hover {
    color: var(--primary-color);
}

/* Nested TOC items are lighter */
#TOC > ul > li > ul a {
    color: var(--text-muted);
    font-size: 0.85rem;
}

#TOC > ul > li > ul a:hover {
    color: var(--primary-color);
}

/* Main Content */
main {
    flex: 1;
    min-width: 0; /* Prevent flex item overflow */
    max-width: var(--max-width);
    padding: 2rem 3rem;
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
    margin-top: 2rem;
    margin-bottom: 1rem;
    font-weight: 600;
    line-height: 1.3;
}

h1 {
    font-size: 2.25rem;
    margin-top: 0;
}

h2 {
    font-size: 1.75rem;
    border-bottom: 2px solid var(--border-color);
    padding-bottom: 0.5rem;
}

h3 {
    font-size: 1.4rem;
}

h4 {
    font-size: 1.15rem;
}

p {
    margin-bottom: 1rem;
}

a {
    color: var(--primary-color);
}

a:hover {
    color: var(--primary-dark);
}

ul, ol {
    margin-bottom: 1rem;
    padding-left: 1.5rem;
}

li {
    margin-bottom: 0.25rem;
}

/* Code Blocks */
pre {
    background: var(--code-bg);
    padding: 1rem;
    border-radius: 8px;
    overflow-x: auto;
    margin: 1rem 0;
    border: 1px solid var(--border-color);
}

code {
    font-family: 'JetBrains Mono', 'Fira Code', 'Consolas', monospace;
    font-size: 0.875rem;
}

p code, li code, td code {
    background: var(--code-bg);
    padding: 0.15rem 0.4rem;
    border-radius: 4px;
    font-size: 0.85em;
}

/* Mermaid Diagrams */
figure {
    margin: 2rem 0;
    text-align: center;
}

figure .mermaid {
    background: transparent;
    padding: 1rem 0;
    border: none;
}

figcaption {
    font-style: italic;
    color: var(--text-muted);
    margin-top: 0.75rem;
    font-size: 0.95rem;
}

/* Regular images */
img {
    max-width: 100%;
    height: auto;
    display: block;
    margin: 1rem auto;
}

/* Tables */
table {
    width: 100%;
    border-collapse: collapse;
    margin: 1.5rem 0;
    font-size: 0.95rem;
}

th, td {
    border: 1px solid var(--border-color);
    padding: 0.75rem 1rem;
    text-align: left;
}

th {
    background: var(--code-bg);
    font-weight: 600;
}

tr:nth-child(even) {
    background: #fafafa;
}

/* Blockquotes */
blockquote {
    border-left: 4px solid var(--primary-color);
    margin: 1rem 0;
    padding: 0.5rem 1rem;
    background: var(--code-bg);
    border-radius: 0 4px 4px 0;
}

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

/* Footer */
footer {
    max-width: var(--max-width);
    margin: 4rem auto 0;
    padding: 2rem;
    border-top: 1px solid var(--border-color);
    text-align: center;
    color: var(--text-muted);
    font-size: 0.9rem;
}

footer p {
    margin-bottom: 0.5rem;
}

/* Responsive */
@media (max-width: 1024px) {
    .sidebar {
        width: 240px;
    }

    main {
        padding: 2rem;
    }
}

@media (max-width: 768px) {
    header {
        padding: 1rem;
    }

    header nav {
        flex-direction: column;
        gap: 0.75rem;
    }

    .layout {
        flex-direction: column;
    }

    .sidebar {
        width: 100%;
        position: static;
        height: auto;
        border-right: none;
        border-bottom: 1px solid var(--border-color);
    }

    #TOC {
        padding: 1rem;
    }

    #TOC h2 {
        cursor: pointer;
        margin-bottom: 0;
        padding-bottom: 0;
        border-bottom: none;
    }

    #TOC > ul {
        display: none;
        margin-top: 1rem;
        padding-top: 1rem;
        border-top: 1px solid var(--border-color);
    }

    #TOC.expanded > ul {
        display: block;
    }

    main {
        padding: 1rem;
    }

    h1 {
        font-size: 1.75rem;
    }

    h2 {
        font-size: 1.5rem;
    }

    table {
        font-size: 0.85rem;
    }

    th, td {
        padding: 0.5rem;
    }
}

/* Print styles */
@media print {
    header, footer, .sidebar {
        display: none;
    }

    .layout {
        display: block;
    }

    main {
        max-width: 100%;
        padding: 0;
    }

    a {
        color: inherit;
        text-decoration: none;
    }

    pre {
        white-space: pre-wrap;
        word-wrap: break-word;
    }
}