:root {
    --primary-color: #007bff;
    --sidebar-bg: #f8f9fa;
    --bg-color: #ffffff;
    --text-color: #333;
    --border-color: #e9ecef;
    --sidebar-width: 280px;
    --right-sidebar-width: 250px;
    --code-bg: #f6f8fa;
    --margin-note-bg: #f9f9f9;
}

[data-theme="dark"] {
    --primary-color: #8ab4f8;
    --sidebar-bg: #252628;
    --bg-color: #1e1e20;
    --text-color: #c9d1d9;
    --border-color: #30363d;
    --code-bg: #2b2d31;
    --margin-note-bg: #2b2d31;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    color: var(--text-color);
    background-color: var(--bg-color);
    line-height: 1.6;
    display: flex;
    min-height: 100vh;
}

.container {
    display: flex;
    width: 100%;
}

/* Left Sidebar */
.sidebar {
    width: var(--sidebar-width);
    background: var(--sidebar-bg);
    border-right: 1px solid var(--border-color);
    height: 100vh;
    position: fixed;
    overflow-y: auto;
    top: 0;
    left: 0;
    padding: 20px;
    transition: transform 0.3s ease;
    z-index: 100;
}

.sidebar-header .logo {
    display: flex;
    align-items: center;
    gap: 10px;
    text-decoration: none;
    color: inherit;
    font-weight: bold;
    font-size: 1.2rem;
    margin-bottom: 2rem;
}

.sidebar-header img {
    max-height: 40px;
}

.nav-list {
    list-style: none;
}

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

.part-title {
    display: block;
    font-weight: 600;
    text-transform: uppercase;
    font-size: 0.85rem;
    color: #6c757d;
    margin-bottom: 0.5rem;
}

.chapter-list {
    list-style: none;
    padding-left: 0;
}

.chapter-item a {
    display: block;
    padding: 0.4rem 0.5rem;
    color: var(--text-color);
    text-decoration: none;
    border-radius: 4px;
    font-size: 0.95rem;
}

.chapter-item a:hover {
    background: rgba(0, 0, 0, 0.05);
    color: var(--primary-color);
}

.chapter-item.active a {
    background: rgba(0, 123, 255, 0.1);
    color: var(--primary-color);
    font-weight: 500;
}

/* Main Content Wrapper */
.content-wrapper {
    margin-left: var(--sidebar-width);
    flex: 1;
    display: flex;
    flex-direction: column;
    min-width: 0;
    position: relative;
}

.content-header {
    padding: 1rem 2rem;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    align-items: center;
}

.icon-button {
    background: none;
    border: none;
    font-size: 1.2rem;
    cursor: pointer;
    display: none;
    margin-right: 15px;
}

/* Page Container (Article + Right Sidebar) */
.page-container {
    display: flex;
    flex: 1;
    max-width: 1400px;
    margin: 0 auto;
    width: 100%;
}

.page-content {
    padding: 2rem 4rem;
    flex: 1;
    min-width: 0;
    /* Important for flex child overflow */
}

/* Right Sidebar (TOC) */
.right-sidebar {
    width: var(--right-sidebar-width);
    padding: 2rem 1rem;
    font-size: 0.9rem;
    border-left: 1px solid transparent;
    /* Optional */
    position: sticky;
    top: 0;
    height: 100vh;
    overflow-y: auto;
    display: none;
    /* Hidden by default on small screens */
}

@media (min-width: 1200px) {
    .right-sidebar {
        display: block;
    }
}

.toc-header {
    font-weight: 600;
    margin-bottom: 1rem;
    color: #495057;
}

.toc-list {
    list-style: none;
    padding: 0;
    border-left: 2px solid var(--border-color);
}

.toc-item a {
    display: block;
    color: var(--text-color);
    opacity: 0.7;
    text-decoration: none;
    padding: 4px 0 4px 15px;
    position: relative;
    transition: all 0.2s;
    font-size: 0.95rem;
}

.toc-item a:hover,
.toc-item.active>a {
    color: var(--primary-color);
    opacity: 1;
}

.toc-item.active>a {
    font-weight: 500;
    border-left: 2px solid var(--primary-color);
    margin-left: -2px;
    /* Pull back to overlap border */
}

/* Collapsible TOC logic */
.toc-level-3 {
    padding-left: 25px;
    display: none;
    /* Hidden by default */
    font-size: 0.9rem;
}

.toc-level-3.expanded {
    display: block;
}

/* Markdown Content Styling Override/Enhancement */
.markdown-body h1,
.markdown-body h2,
.markdown-body h3 {
    margin-top: 2rem;
    margin-bottom: 1rem;
}

.markdown-body h1 {
    margin-top: 2.5rem;
}

.markdown-body a {
    color: var(--primary-color);
    text-decoration: none;
}

.markdown-body a:hover {
    text-decoration: underline;
}

.markdown-body img {
    max-width: 100%;
    height: auto;
}

.markdown-body ul,
.markdown-body ol {
    padding-left: 2rem;
    margin-left: 1rem;
    /* Extra indentation */
    margin-bottom: 1rem;
}

.markdown-body li {
    margin-bottom: 0.25rem;
}

.markdown-body pre {
    padding: 1rem;
    border-radius: 6px;
    overflow-x: auto;
    background-color: var(--code-bg);
    /* Fallback */
}

.margin-note {
    float: right;
    clear: right;
    width: 30%;
    margin: 0 0 1rem 1rem;
    padding: 0.8rem;
    background-color: var(--margin-note-bg);
    border-left: 4px solid var(--primary-color);
    font-size: 0.9em;
    color: var(--text-color);
    opacity: 0.9;
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
    border-radius: 4px;
}

/* Header Controls */
.header-controls {
    margin-left: auto;
    display: flex;
    gap: 10px;
    align-items: center;
}

.header-controls .icon-button {
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--text-color);
    text-decoration: none;
    font-size: 1.2rem;
    padding: 5px;
    width: 32px;
    height: 32px;
    cursor: pointer;
    background: none;
    border: none;
    transition: color 0.2s;
}

.header-controls .icon-button:hover {
    color: var(--primary-color);
}


/* On small screens, disable float and make it full width or block */
@media (max-width: 900px) {
    .margin-note {
        float: none;
        width: 100%;
        margin: 1rem 0;
    }
}

/* MathJax Overlay Fix (optional) */
mjx-container {
    overflow-x: auto;
    overflow-y: hidden;
    max-width: 100%;
}

.content-footer {
    padding: 2rem;
    text-align: center;
    color: #6c757d;
    font-size: 0.9rem;
    border-top: 1px solid var(--border-color);
    margin-top: auto;
}

/* Responsive */
@media (max-width: 768px) {
    .sidebar {
        transform: translateX(-100%);
        box-shadow: 2px 0 5px rgba(0, 0, 0, 0.1);
    }

    .sidebar.open {
        transform: translateX(0);
    }

    .content-wrapper {
        margin-left: 0;
    }

    .icon-button {
        display: block;
    }

    .page-content {
        padding: 1.5rem;
    }

    .right-sidebar {
        display: none !important;
    }
}