@import url('https://fonts.googleapis.com/css2?family=JetBrains+Mono:wght@400;600&family=Syne:wght@400;600;700;800&family=DM+Sans:wght@300;400;500&display=swap');

:root {
    --bg: #0d0f14;
    --surface: #13161e;
    --surface2: #1a1e29;
    --border: #252a38;
    --accent: #00e5ff;
    --accent2: #7c3aed;
    --accent3: #f59e0b;
    --accent4: #10b981;
    --accent5: #ef4444;
    --text: #e2e8f0;
    --muted: #64748b;
    --code-bg: #0a0c10;
}

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

body {
    background: var(--bg);
    color: var(--text);
    font-family: 'DM Sans', sans-serif;
    font-size: 15px;
    line-height: 1.7;
    display: flex;
}

/* ── SIDEBAR ── */
#sidebar {
    width: 280px;
    min-height: 100vh;
    background: var(--surface);
    border-right: 1px solid var(--border);
    position: fixed;
    top: 0;
    left: 0;
    overflow-y: auto;
    z-index: 100;
}

#sidebar::-webkit-scrollbar {
    width: 4px;
}

#sidebar::-webkit-scrollbar-track {
    background: transparent;
}

#sidebar::-webkit-scrollbar-thumb {
    background: var(--border);
    border-radius: 2px;
}

.sidebar-header {
    padding: 24px 20px;
    border-bottom: 1px solid var(--border);
    background: linear-gradient(135deg, #0d0f14, #1a1e29);
}

.sidebar-header h1 {
    font-family: 'Syne', sans-serif;
    font-size: 18px;
    font-weight: 800;
    background: linear-gradient(90deg, var(--accent), var(--accent2));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.sidebar-header p {
    font-size: 11px;
    color: var(--muted);
    margin-top: 4px;
}

.nav-section {
    padding: 8px 0;
    border-bottom: 1px solid var(--border);
}

.nav-section-title {
    padding: 10px 20px 4px;
    font-size: 10px;
    font-weight: 700;
    letter-spacing: 1.5px;
    text-transform: uppercase;
    color: var(--muted);
}

.nav-link {
    display: block;
    padding: 6px 20px;
    font-size: 12.5px;
    color: var(--muted);
    text-decoration: none;
    transition: all 0.15s;
    border-left: 2px solid transparent;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

.nav-link:hover,
.nav-link.active {
    color: var(--accent);
    border-left-color: var(--accent);
    background: rgba(0, 229, 255, 0.05);
}

.nav-link span.num {
    color: var(--accent2);
    font-family: 'JetBrains Mono', monospace;
    font-size: 10px;
    margin-right: 6px;
}

/* ── MAIN CONTENT ── */
#main {
    margin-left: 280px;
    flex: 1;
    padding: 0 0 80px;
}

.hero {
    background: linear-gradient(135deg, #0d0f14 0%, #1a1029 50%, #0d1420 100%);
    padding: 60px 60px 50px;
    border-bottom: 1px solid var(--border);
    position: relative;
    overflow: hidden;
}

.hero::before {
    content: '';
    position: absolute;
    top: -100px;
    right: -100px;
    width: 400px;
    height: 400px;
    background: radial-gradient(circle, rgba(124, 58, 237, 0.15) 0%, transparent 70%);
    pointer-events: none;
}

.hero::after {
    content: '';
    position: absolute;
    bottom: -80px;
    left: 200px;
    width: 300px;
    height: 300px;
    background: radial-gradient(circle, rgba(0, 229, 255, 0.1) 0%, transparent 70%);
    pointer-events: none;
}

.hero h1 {
    font-family: 'Syne', sans-serif;
    font-size: 42px;
    font-weight: 800;
    line-height: 1.2;
    background: linear-gradient(90deg, #fff 0%, var(--accent) 50%, var(--accent2) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero p {
    color: var(--muted);
    margin-top: 12px;
    max-width: 600px;
    font-size: 16px;
}

.hero-badges {
    display: flex;
    gap: 10px;
    flex-wrap: wrap;
    margin-top: 20px;
}

.badge {
    padding: 4px 12px;
    border-radius: 20px;
    font-size: 12px;
    font-weight: 500;
    border: 1px solid;
}

.badge-cyan {
    border-color: var(--accent);
    color: var(--accent);
    background: rgba(0, 229, 255, 0.08);
}

.badge-purple {
    border-color: var(--accent2);
    color: #a78bfa;
    background: rgba(124, 58, 237, 0.08);
}

.badge-amber {
    border-color: var(--accent3);
    color: var(--accent3);
    background: rgba(245, 158, 11, 0.08);
}

.badge-green {
    border-color: var(--accent4);
    color: var(--accent4);
    background: rgba(16, 185, 129, 0.08);
}

/* ── TOPIC ── */
.topic {
    padding: 50px 60px;
    border-bottom: 1px solid var(--border);
    scroll-margin-top: 20px;
}

.topic:nth-child(even) {
    background: rgba(255, 255, 255, 0.01);
}

.topic-header {
    display: flex;
    align-items: flex-start;
    gap: 16px;
    margin-bottom: 30px;
}

.topic-num {
    font-family: 'JetBrains Mono', monospace;
    font-size: 12px;
    color: var(--accent2);
    background: rgba(124, 58, 237, 0.1);
    border: 1px solid rgba(124, 58, 237, 0.3);
    padding: 4px 10px;
    border-radius: 6px;
    white-space: nowrap;
    margin-top: 4px;
}

.topic h2 {
    font-family: 'Syne', sans-serif;
    font-size: 26px;
    font-weight: 700;
    color: #fff;
}

.topic h2 .phase-tag {
    font-size: 12px;
    font-weight: 500;
    padding: 2px 10px;
    border-radius: 4px;
    margin-left: 12px;
    vertical-align: middle;
}

/* ── SECTIONS ── */
.section {
    margin: 24px 0;
}

.section-title {
    font-family: 'Syne', sans-serif;
    font-size: 13px;
    font-weight: 700;
    letter-spacing: 1px;
    text-transform: uppercase;
    margin-bottom: 12px;
    display: flex;
    align-items: center;
    gap: 8px;
}

.section-title::after {
    content: '';
    flex: 1;
    height: 1px;
    background: var(--border);
}

.st-def {
    color: var(--accent);
}

.st-int {
    color: var(--accent4);
}

.st-type {
    color: var(--accent3);
}

.st-step {
    color: #a78bfa;
}

.st-code {
    color: var(--accent);
}

.st-err {
    color: var(--accent5);
}

.st-int2 {
    color: var(--accent3);
}

.st-sum {
    color: var(--accent4);
}

.st-task {
    color: #f472b6;
}

.section p {
    color: #cbd5e1;
    line-height: 1.8;
    margin-bottom: 10px;
}

.section ul,
.section ol {
    padding-left: 20px;
    color: #cbd5e1;
}

.section li {
    margin-bottom: 6px;
}

.section strong {
    color: #fff;
}

/* ── CODE BLOCKS ── */
.code-block {
    background: var(--code-bg);
    border: 1px solid var(--border);
    border-radius: 10px;
    overflow: hidden;
    margin: 16px 0;
}

.code-header {
    background: var(--surface2);
    padding: 8px 16px;
    font-size: 11px;
    color: var(--muted);
    font-family: 'JetBrains Mono', monospace;
    display: flex;
    align-items: center;
    gap: 8px;
    border-bottom: 1px solid var(--border);
}

.code-dot {
    width: 10px;
    height: 10px;
    border-radius: 50%;
}

.cd1 {
    background: #ef4444;
}

.cd2 {
    background: #f59e0b;
}

.cd3 {
    background: #10b981;
}

.code-block pre {
    padding: 20px;
    font-family: 'JetBrains Mono', monospace;
    font-size: 13px;
    line-height: 1.7;
    overflow-x: auto;
    color: #e2e8f0;
}

.code-block pre::-webkit-scrollbar {
    height: 4px;
}

.code-block pre::-webkit-scrollbar-track {
    background: transparent;
}

.code-block pre::-webkit-scrollbar-thumb {
    background: var(--border);
}

/* Syntax highlighting */
.kw {
    color: #c792ea;
}

/* keywords */
.fn {
    color: #82aaff;
}

/* functions */
.st {
    color: #c3e88d;
}

/* strings */
.cm {
    color: #546e7a;
    font-style: italic;
}

/* comments */
.nm {
    color: #f78c6c;
}

/* numbers */
.cl {
    color: #ffcb6b;
}

/* class names */
.op {
    color: #89ddff;
}

/* operators */
.bi {
    color: #00bcd4;
}

/* builtins */

/* ── CALLOUT BOXES ── */
.callout {
    border-radius: 8px;
    padding: 16px 20px;
    margin: 16px 0;
    border-left: 3px solid;
    font-size: 14px;
}

.callout-info {
    background: rgba(0, 229, 255, 0.06);
    border-color: var(--accent);
}

.callout-warn {
    background: rgba(245, 158, 11, 0.06);
    border-color: var(--accent3);
}

.callout-danger {
    background: rgba(239, 68, 68, 0.06);
    border-color: var(--accent5);
}

.callout-success {
    background: rgba(16, 185, 129, 0.06);
    border-color: var(--accent4);
}

.callout-title {
    font-weight: 600;
    margin-bottom: 6px;
    font-size: 13px;
}

/* ── TABLE ── */
table {
    width: 100%;
    border-collapse: collapse;
    margin: 16px 0;
    font-size: 13.5px;
}

th {
    background: var(--surface2);
    padding: 10px 14px;
    text-align: left;
    font-weight: 600;
    color: var(--accent);
    border: 1px solid var(--border);
    font-family: 'Syne', sans-serif;
    font-size: 12px;
    letter-spacing: 0.5px;
}

td {
    padding: 8px 14px;
    border: 1px solid var(--border);
    color: #cbd5e1;
    vertical-align: top;
}

tr:nth-child(even) td {
    background: rgba(255, 255, 255, 0.02);
}

/* ── FORMULA ── */
.formula {
    background: var(--surface2);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 14px 20px;
    font-family: 'JetBrains Mono', monospace;
    font-size: 14px;
    color: var(--accent3);
    text-align: center;
    margin: 12px 0;
}

/* ── TASK BOX ── */
.task-box {
    background: linear-gradient(135deg, rgba(244, 114, 182, 0.08), rgba(124, 58, 237, 0.08));
    border: 1px solid rgba(244, 114, 182, 0.3);
    border-radius: 10px;
    padding: 20px;
    margin-top: 16px;
}

.task-box .task-title {
    font-family: 'Syne', sans-serif;
    font-weight: 700;
    color: #f472b6;
    margin-bottom: 10px;
    font-size: 14px;
}

/* ── INTERVIEW BOX ── */
.interview-box {
    background: rgba(245, 158, 11, 0.06);
    border: 1px solid rgba(245, 158, 11, 0.25);
    border-radius: 10px;
    padding: 18px;
    margin: 16px 0;
}

.interview-box .q {
    font-weight: 600;
    color: var(--accent3);
    margin-bottom: 6px;
    font-size: 13.5px;
}

.interview-box .a {
    color: #cbd5e1;
    font-size: 13.5px;
}

/* ── SUMMARY BULLETS ── */
.summary-list {
    list-style: none;
    padding: 0;
}

.summary-list li {
    padding: 6px 0 6px 24px;
    position: relative;
    color: #cbd5e1;
}

.summary-list li::before {
    content: '→';
    position: absolute;
    left: 0;
    color: var(--accent4);
    font-weight: 700;
}

/* ── DIVIDER ── */
.phase-divider {
    padding: 20px 60px;
    background: var(--surface2);
    border-bottom: 1px solid var(--border);
    border-top: 1px solid var(--border);
    display: flex;
    align-items: center;
    gap: 16px;
}

.phase-divider h3 {
    font-family: 'Syne', sans-serif;
    font-size: 14px;
    font-weight: 700;
    letter-spacing: 2px;
    text-transform: uppercase;
}

.phase-divider::before {
    content: '';
    width: 30px;
    height: 2px;
    background: currentColor;
}

/* ── RESPONSIVE ── */
@media (max-width: 900px) {
    #sidebar {
        display: none;
    }

    #main {
        margin-left: 0;
    }

    .topic {
        padding: 30px 20px;
    }

    .hero {
        padding: 30px 20px;
    }
}