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

body {
    font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
    transition: background 0.25s ease, color 0.25s ease;
}

body.theme-dark {
    background: #020617;
    color: #e5e7eb;
}

body.theme-light {
    background: #f9fafb;
    color: #0f172a;
}

/* ============ CONTAINER & HEADER ============ */
.chapter-container {
    max-width: 1280px;
    margin: 0 auto;
    padding: 1.5rem 1rem 3rem;
}

.chapter-header {
    margin-bottom: 1.5rem;
    display: flex;
    flex-direction: column;
    gap: 0.25rem;
    position: sticky;
    top: 0;
    z-index: 10;
    padding-bottom: 0.75rem;
    background: linear-gradient(to bottom,
    rgba(2,6,23,0.98),
    rgba(2,6,23,0.9),
    transparent);
    backdrop-filter: blur(12px);
}

body.theme-light .chapter-header {
    background: linear-gradient(to bottom,
    rgba(249,250,251,0.98),
    rgba(249,250,251,0.9),
    transparent);
}

.chapter-header-top {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.chapter-breadcrumb {
    font-size: 0.85rem;
    color: #94a3b8;
}
body.theme-light .chapter-breadcrumb {
    color: #6b7280;
}

.chapter-header h1 {
    font-size: 1.8rem;
}

.chapter-subtitle {
    font-size: 0.95rem;
    color: #9ca3af;
}
body.theme-light .chapter-subtitle {
    color: #4b5563;
}

/* Theme toggle */
.theme-toggle-btn {
    border-radius: 999px;
    border: 1px solid #1f2937;
    background: #020617;
    color: #e5e7eb;
    padding: 0.35rem 0.8rem;
    font-size: 0.85rem;
    cursor: pointer;
}
body.theme-light .theme-toggle-btn {
    background: #e5e7eb;
    color: #0f172a;
    border-color: #d1d5db;
}

/* ============ LAYOUT ============ */
.chapter-layout {
    display: grid;
    grid-template-columns: 260px minmax(0, 1fr);
    gap: 1.5rem;
}

@media (max-width: 900px) {
    .chapter-layout {
        grid-template-columns: 1fr;
    }
}

/* ============ SIDEBAR ============ */
.chapter-sidebar {
    position: sticky;
    top: 3.4rem;
    align-self: flex-start;
    max-height: calc(100vh - 3.4rem);
    overflow-y: auto;
    padding-right: 0.5rem;
}

.sidebar-box {
    background: #020617;
    border-radius: 0.9rem;
    border: 1px solid #1f2937;
    padding: 1rem;
}
body.theme-light .sidebar-box {
    background: #ffffff;
    border-color: #e5e7eb;
}

.chapter-sidebar h3 {
    font-size: 0.9rem;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    color: #9ca3af;
    margin-bottom: 0.6rem;
}

/* Sidebar search */
.sidebar-search {
    margin-bottom: 0.7rem;
}
.sidebar-search input {
    width: 100%;
    padding: 0.35rem 0.6rem;
    border-radius: 0.5rem;
    border: 1px solid #1f2937;
    background: #020617;
    color: #e5e7eb;
    font-size: 0.85rem;
}
body.theme-light .sidebar-search input {
    background: #f9fafb;
    color: #0f172a;
    border-color: #e5e7eb;
}

/* Sidebar nav */
.chapter-sidebar nav a {
    display: block;
    padding: 0.45rem 0.6rem;
    margin-bottom: 0.25rem;
    border-radius: 0.6rem;
    font-size: 0.9rem;
    color: #e5e7eb;
    border-left: 3px solid transparent;
    text-decoration: none;
    transition: background 0.2s, color 0.2s, border-color 0.2s;
}
body.theme-light .chapter-sidebar nav a {
    color: #0f172a;
}

.chapter-sidebar nav a:hover {
    background: rgba(56,189,248,0.15);
    color: #38bdf8;
}

.chapter-sidebar nav a.active {
    background: rgba(56,189,248,0.25);
    border-left-color: #38bdf8;
    color: #38bdf8;
}

.chapter-sidebar nav a.hidden {
    display: none;
}

/* ============ MAIN CONTENT ============ */
.chapter-main {
    min-width: 0;
}

.chapter-card {
    background: #020617;
    border-radius: 0.9rem;
    border: 1px solid #1f2937;
    padding: 1.25rem 1.35rem;
    margin-bottom: 1.3rem;
    scroll-margin-top: 4.5rem;
}
body.theme-light .chapter-card {
    background: #ffffff;
    border-color: #e5e7eb;
}

.chapter-card h2 {
    font-size: 1.35rem;
    margin-bottom: 0.5rem;
    color: #38bdf8;
}
.chapter-card h3 {
    font-size: 1.02rem;
    margin: 0.7rem 0 0.3rem;
}

.chapter-card p {
    font-size: 0.95rem;
    margin-bottom: 0.4rem;
}

/* Chip */
.chapter-chip {
    display: inline-block;
    font-size: 0.75rem;
    padding: 0.18rem 0.6rem;
    border-radius: 999px;
    border: 1px solid #38bdf8;
    background: rgba(56,189,248,0.12);
    color: #38bdf8;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    margin-bottom: 0.4rem;
}

/* Lists */
.chapter-list {
    margin-left: 1.1rem;
    margin-top: 0.3rem;
    font-size: 0.95rem;
}
.chapter-list li {
    margin-bottom: 0.35rem;
}

/* Note */
.chapter-note {
    margin-top: 0.7rem;
    padding: 0.6rem 0.75rem;
    border-left: 3px solid #38bdf8;
    background: #020617;
    color: #9ca3af;
    font-size: 0.9rem;
}
body.theme-light .chapter-note {
    background: #f1f5f9;
    color: #4b5563;
}

/* ============ CODE EDITOR ============ */
.code-editor {
    position: relative;
    margin: 0.8rem 0;
    border-radius: 0.75rem;
    border: 1px solid #1f2937;
    overflow: hidden;
    background: #0b1120;
}

.code-editor pre {
    margin: 0;
    background: #0b1120 !important;
}

/* Prism base */
code[class*="language-"],
pre[class*="language-"] {
    font-family: "JetBrains Mono", Consolas, monospace;
    font-size: 0.9rem;
}

/* Line numbers gutter */
pre.line-numbers {
    padding-left: 3.2em;
}
.line-numbers .line-numbers-rows {
    border-right: 1px solid #1f2937;
}
.line-numbers .line-numbers-rows > span:before {
    color: #64748b;
}

/* Copy button */
.copy-btn {
    position: absolute;
    top: 0.55rem;
    right: 0.7rem;
    font-size: 0.75rem;
    padding: 0.18rem 0.6rem;
    border-radius: 0.5rem;
    border: 1px solid #334155;
    background: rgba(15,23,42,0.95);
    color: #e5e7eb;
    cursor: pointer;
    opacity: 0;
    transform: translateY(-2px);
    transition: opacity 0.15s ease, transform 0.15s ease, background 0.2s;
}
.code-editor:hover .copy-btn {
    opacity: 1;
    transform: translateY(0);
}
.copy-btn.copied {
    background: #16a34a;
    border-color: #16a34a;
}

/* ============ FOOTER ============ */
.chapter-footer {
    margin-top: 2rem;
    padding-top: 1rem;
    border-top: 1px solid #1f2937;
    text-align: center;
    font-size: 0.8rem;
    color: #6b7280;
}
body.theme-light .chapter-footer {
    border-color: #e5e7eb;
    color: #9ca3af;
}