:root {
    --primary-color: #2563eb;
    --text-color: #333;
    --bg-color: #fff;
    --sidebar-width: 300px;
    --font-heading: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
    --font-body: 'Merriweather', 'Georgia', serif;
}

* { box-sizing: border-box; }

body {
    margin: 0;
    font-family: var(--font-body);
    color: var(--text-color);
    background: var(--bg-color);
    line-height: 1.8;
}

h1, h2, h3, h4, h5, h6 {
    font-family: var(--font-heading);
    color: #111;
    margin-top: 2em;
    margin-bottom: 0.5em;
    font-weight: 700;
}

h1 { font-size: 2.2rem; border-bottom: 2px solid #eee; padding-bottom: 0.5rem; }
h2 { font-size: 1.6rem; }
h3 { font-size: 1.3rem; }

p { margin-bottom: 1.5em; }

a { color: var(--primary-color); text-decoration: none; transition: color 0.2s; }
a:hover { color: #1d4ed8; text-decoration: underline; }

ul, ol { margin-bottom: 1.5em; padding-left: 2em; }
li { margin-bottom: 0.5em; }

mark { background: #fef3c7; padding: 0 0.2em; }

.layout {
    display: flex;
    max-width: 1400px;
    margin: 0 auto;
    min-height: 100vh;
}

.sidebar {
    width: var(--sidebar-width);
    position: sticky;
    top: 0;
    height: 100vh;
    overflow-y: auto;
    padding: 2rem;
    border-right: 1px solid #eee;
    background: #f8fafc;
    flex-shrink: 0;
}

.sidebar header h2 {
    font-size: 1.2rem;
    margin-top: 0;
    color: #0f172a;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.sidebar nav ul {
    list-style: none;
    padding: 0;
    margin: 0;
}

.sidebar nav ul li {
    margin: 0;
}

.sidebar nav ul li a {
    display: block;
    padding: 0.5rem 0;
    color: #64748b;
    font-size: 0.95rem;
    border-bottom: 1px solid transparent;
    font-family: var(--font-heading);
}

.sidebar nav ul li a:hover {
    color: var(--primary-color);
}

.sidebar nav .toc-h1 { font-weight: bold; margin-top: 1rem; color: #334155; }
.sidebar nav .toc-h2 { padding-left: 1rem; font-size: 0.9rem; }
.sidebar nav .toc-h3 { padding-left: 2rem; font-size: 0.85rem; }

.content {
    flex: 1;
    padding: 4rem 6rem;
    max-width: 900px;
}

/* Responsive */
@media (max-width: 900px) {
    .layout { flex-direction: column; }
    .sidebar { width: 100%; height: auto; position: relative; border-right: none; border-bottom: 1px solid #eee; padding: 1rem; }
    .content { padding: 2rem; }
}