:root {
    /* Palette colors:
       #F8F9FA, #E9ECEF, #DEE2E6, #CED4DA, #ADB5BD, #6C757D, #495057, #343A40, #212529
    */
    --bg-page: #F8F9FA;
    --bg-sidebar: #E9ECEF;
    --bg-hover: #DEE2E6;
    --bg-active: #CED4DA;
    --bg-code: #E9ECEF;
    
    --border-color: #DEE2E6;
    --border-strong: #CED4DA;
    
    --text-primary: #212529;
    --text-body: #343A40;
    --text-muted: #6C757D;

    --font-display: 'Space Grotesk', -apple-system, BlinkMacSystemFont, sans-serif;
    --font-body: 'Plus Jakarta Sans', -apple-system, BlinkMacSystemFont, sans-serif;
    --font-mono: 'JetBrains Mono', monospace;

    --radius-sm: 4px;
    --radius-md: 6px;

    --toggle-bg: #343A40;
    --toggle-border: #212529;

    color-scheme: light;
}

[data-theme="dark"] {
    --bg-page: #212529;
    --bg-sidebar: #343A40;
    --bg-hover: #495057;
    --bg-active: #495057;
    --bg-code: #343A40;
    
    --border-color: #495057;
    --border-strong: #6C757D;
    
    --text-primary: #F8F9FA;
    --text-body: #DEE2E6;
    --text-muted: #ADB5BD;

    --toggle-bg: #F8F9FA;
    --toggle-border: #E9ECEF;

    color-scheme: dark;
}

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

body {
    background-color: var(--bg-page);
    color: var(--text-body);
    font-family: var(--font-body);
    line-height: 1.6;
    height: 100vh;
    overflow: hidden;
    transition: background-color 0.2s ease, color 0.2s ease;
}

.layout {
    display: flex;
    height: 100vh;
    width: 100vw;
}

/* --- Sidebar --- */
.sidebar {
    width: 300px;
    background: var(--bg-sidebar);
    border-right: 1px solid var(--border-color);
    display: flex;
    flex-direction: column;
    flex-shrink: 0;
    transition: background-color 0.2s ease, border-color 0.2s ease;
}

.brand {
    padding: 1.5rem 1.5rem 1.25rem;
    border-bottom: 1px solid var(--border-color);
}

.brand h1 {
    font-family: var(--font-display);
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--text-primary);
    letter-spacing: -0.02em;
    line-height: 1.2;
}

.brand .tagline {
    font-family: var(--font-mono);
    font-size: 0.72rem;
    font-weight: 500;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.08em;
    margin-top: 0.35rem;
}

.nav-container {
    flex: 1;
    overflow-y: auto;
    padding: 1.25rem 0.75rem;
    scrollbar-color: var(--border-strong) transparent;
}

.nav-group {
    margin-bottom: 1.5rem;
}

.group-title {
    font-family: var(--font-mono);
    font-size: 0.7rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--text-muted);
    padding: 0.4rem 0.75rem;
    margin-bottom: 0.2rem;
}

.nav-item {
    display: flex;
    align-items: center;
    padding: 0.45rem 0.75rem;
    margin-bottom: 0.2rem;
    color: var(--text-body);
    text-decoration: none;
    font-family: var(--font-body);
    font-size: 0.9rem;
    font-weight: 500;
    border-radius: var(--radius-sm);
    transition: background-color 0.15s ease, color 0.15s ease;
    cursor: pointer;
}

.nav-item:hover {
    background: var(--bg-hover);
    color: var(--text-primary);
}

.nav-item.active {
    background: var(--bg-active);
    color: var(--text-primary);
    font-weight: 600;
}

/* Sidebar Footer & Inline Toggle Button */
.sidebar-footer {
    padding: 1rem 1.5rem;
    border-top: 1px solid var(--border-color);
    background: var(--bg-sidebar);
}

.footer-links {
    display: flex;
    align-items: center;
    gap: 1rem;
}

.footer-links a {
    font-family: var(--font-mono);
    font-size: 0.8rem;
    font-weight: 500;
    color: var(--text-muted);
    text-decoration: none;
    transition: color 0.15s ease;
}

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

.theme-toggle-btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    margin-left: auto;
    width: 20px;
    height: 20px;
    padding: 0;
    background: transparent;
    border: none;
    cursor: pointer;
    outline: none;
}

.theme-indicator {
    width: 14px;
    height: 14px;
    border-radius: 50%;
    background: var(--toggle-bg);
    border: 1px solid var(--toggle-border);
    transition: transform 0.2s ease, background-color 0.2s ease;
}

.theme-toggle-btn:hover .theme-indicator {
    transform: scale(1.15);
}

/* --- Right Zone: Content --- */
.content-zone {
    flex: 1;
    overflow-y: auto;
    background: var(--bg-page);
    padding: 3rem 4rem;
    scrollbar-color: var(--border-strong) transparent;
    transition: background-color 0.2s ease;
}

.markdown-body {
    max-width: 780px;
    margin: 0 auto;
}

/* Typography in Markdown */
.markdown-body h1 {
    font-family: var(--font-display);
    font-size: 2.2rem;
    font-weight: 700;
    color: var(--text-primary);
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 0.6rem;
    margin-bottom: 1.5rem;
    letter-spacing: -0.02em;
}

.markdown-body h2 {
    font-family: var(--font-display);
    font-size: 1.35rem;
    font-weight: 600;
    color: var(--text-primary);
    margin: 2rem 0 1rem;
    letter-spacing: -0.01em;
}

.markdown-body h3 {
    font-family: var(--font-body);
    font-size: 1.15rem;
    font-weight: 600;
    color: var(--text-primary);
    margin: 1.5rem 0 0.8rem;
}

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

.markdown-body ul, .markdown-body ol {
    margin-bottom: 1.25rem;
    padding-left: 1.5rem;
    color: var(--text-body);
}

.markdown-body li {
    margin-bottom: 0.35rem;
}

.markdown-body code {
    font-family: var(--font-mono);
    background: var(--bg-code);
    color: var(--text-primary);
    padding: 0.2rem 0.4rem;
    border-radius: var(--radius-sm);
    font-size: 0.85em;
    border: 1px solid var(--border-color);
}

.markdown-body pre {
    background: var(--bg-code);
    border: 1px solid var(--border-color);
    padding: 1.1rem 1.25rem;
    border-radius: var(--radius-md);
    overflow-x: auto;
    margin-bottom: 1.4rem;
}

.markdown-body pre code {
    padding: 0;
    color: var(--text-body);
    background: none;
    border: none;
    font-size: 0.88em;
}

.markdown-body blockquote {
    font-family: var(--font-body);
    font-style: italic;
    font-size: 1.05rem;
    background: var(--bg-sidebar);
    border-left: 3px solid var(--border-strong);
    border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
    padding: 0.85rem 1.25rem;
    color: var(--text-muted);
    margin-bottom: 1.4rem;
}

.loading {
    font-family: var(--font-mono);
    font-size: 0.9rem;
    color: var(--text-muted);
}

/* Responsive adjustments */
@media (max-width: 768px) {
    .layout {
        flex-direction: column;
    }
    .sidebar {
        width: 100%;
        height: auto;
        border-right: none;
        border-bottom: 1px solid var(--border-color);
    }
    .content-zone {
        padding: 1.75rem 1.25rem;
    }
}