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

:root {
  --ms-blue: #0078d4;
  --ms-blue-dark: #005a9e;
  --ms-blue-light: #1890f1;
  --ms-purple: #7719aa;
  --ms-cyan: #00bcf2;
  --bg: #0a0d12;
  --bg2: #0e1118;
  --surface: #13171f;
  --surface2: #181c26;
  --border: #1e2535;
  --border2: #252d3d;
  --text: #c8cdd8;
  --text-dim: #6b7590;
  --white: #eef2fa;
  --accent: #50e6ff;
}

html {
  scroll-behavior: smooth;
}

body {
  background: var(--bg);
  color: var(--text);
  font-family: "Segoe UI", system-ui, sans-serif;
  overflow-x: hidden;
  line-height: 1.7;
}

a {
  color: var(--ms-blue-light);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

.progress-bar {
  height: 3px;
  background: linear-gradient(90deg, var(--ms-blue), var(--accent));
  border-radius: 0;
}

nav {
  position: sticky;
  top: 0;
  z-index: 200;
  background: rgba(10, 13, 18, 0.92);
  backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border);
}

.nav-inner {
  max-width: 1100px;
  margin: 0 auto;
  padding: 0 32px;
  display: flex;
  align-items: center;
  height: 52px;
  gap: 12px;
}

.nav-logo {
  display: flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  margin-right: auto;
}

.nav-logo-text {
  font-family: "Rajdhani", sans-serif;
  font-weight: 700;
  font-size: 1rem;
  color: var(--white);
  letter-spacing: 0.02em;
}

.nav-logo-text span {
  color: var(--ms-blue-light);
}

.nav-link {
  color: var(--text-dim);
  font-size: 0.83rem;
  padding: 6px 14px;
  border-radius: 3px;
  transition: all 0.15s;
  text-decoration: none;
}

.nav-link:hover {
  color: var(--white);
  background: rgba(255, 255, 255, 0.05);
  text-decoration: none;
}

.lesson-wrap {
  max-width: 860px;
  margin: 0 auto;
  padding: 48px 32px 80px;
}

.lesson-eyebrow {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 28px;
  flex-wrap: wrap;
}

.lesson-count {
  font-family: "JetBrains Mono", monospace;
  font-size: 0.7rem;
  color: var(--text-dim);
}

.lesson-category {
  font-size: 0.7rem;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--ms-blue-light);
  font-family: "JetBrains Mono", monospace;
  background: rgba(0, 120, 212, 0.12);
  border: 1px solid rgba(0, 120, 212, 0.3);
  padding: 3px 12px;
  border-radius: 100px;
}

.lesson-level {
  font-size: 0.7rem;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  padding: 3px 12px;
  border-radius: 100px;
  background: rgba(255, 255, 255, 0.06);
  color: var(--text-dim);
}

.lesson-duration {
  font-size: 0.72rem;
  color: var(--text-dim);
  font-family: "JetBrains Mono", monospace;
}

.lesson-duration::before {
  content: "⏱ ";
}

.lesson-title {
  font-family: "Rajdhani", sans-serif;
  font-weight: 700;
  font-size: clamp(1.8rem, 4vw, 2.8rem);
  color: var(--white);
  line-height: 1.1;
  margin-bottom: 16px;
  letter-spacing: -0.01em;
}

.lesson-intro {
  font-size: 1.05rem;
  color: var(--text-dim);
  border-left: 3px solid var(--ms-blue);
  padding-left: 16px;
  margin-bottom: 48px;
  line-height: 1.7;
}

.lesson-section {
  margin-bottom: 48px;
}

.lesson-section h2 {
  font-family: "Rajdhani", sans-serif;
  font-weight: 700;
  font-size: 1.3rem;
  color: var(--white);
  margin-bottom: 16px;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--border);
  display: flex;
  align-items: center;
  gap: 10px;
}

.lesson-section h2::before {
  content: "";
  width: 4px;
  height: 1.2em;
  background: var(--ms-blue);
  border-radius: 2px;
  display: inline-block;
  flex-shrink: 0;
}

.lesson-section p,
.lesson-section ul,
.lesson-section ol {
  font-size: 0.95rem;
  color: var(--text);
  line-height: 1.8;
}

.lesson-section ul,
.lesson-section ol {
  padding-left: 1.5rem;
}

.lesson-section li {
  margin-bottom: 4px;
}

.code-block {
  background: #1e1e1e;
  border: 1px solid var(--border2);
  border-radius: 6px;
  padding: 20px;
  font-family: "JetBrains Mono", monospace;
  font-size: 0.8rem;
  line-height: 1.8;
  overflow-x: auto;
  margin: 16px 0;
  position: relative;
  color: #dcdcdc;
}

.code-block::before {
  content: "Code";
  position: absolute;
  top: 8px;
  right: 12px;
  font-size: 0.62rem;
  color: var(--text-dim);
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

code {
  background: var(--surface2);
  padding: 1px 6px;
  border-radius: 3px;
  font-family: "JetBrains Mono", monospace;
  font-size: 0.82rem;
  color: var(--accent);
}

kbd {
  background: var(--surface2);
  border: 1px solid var(--border2);
  border-radius: 3px;
  padding: 1px 6px;
  font-family: "JetBrains Mono", monospace;
  font-size: 0.78rem;
  color: var(--white);
}

.lesson-table {
  width: 100%;
  border-collapse: collapse;
  margin: 16px 0;
  font-size: 0.88rem;
}

.lesson-table th {
  background: var(--surface2);
  color: var(--white);
  font-family: "Rajdhani", sans-serif;
  font-weight: 600;
  padding: 10px 14px;
  text-align: left;
  border: 1px solid var(--border2);
}

.lesson-table td {
  padding: 9px 14px;
  border: 1px solid var(--border);
  color: var(--text);
}

.lesson-table tr:hover td {
  background: rgba(255, 255, 255, 0.02);
}

.lesson-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 28px 0;
  border-top: 1px solid var(--border);
  margin-top: 48px;
  gap: 16px;
  flex-wrap: wrap;
}

.lesson-nav a {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 10px 20px;
  background: var(--surface);
  border: 1px solid var(--border2);
  border-radius: 4px;
  color: var(--text);
  font-size: 0.85rem;
  transition: all 0.15s;
  text-decoration: none;
}

.lesson-nav a:hover {
  border-color: var(--ms-blue);
  color: var(--white);
  text-decoration: none;
}

.lesson-nav .prev::before {
  content: "←";
}

.lesson-nav .next::after {
  content: "→";
}

.book-promo-wrap {
  margin-top: 48px;
}

.book-promo {
  margin: 48px 0;
}

.book-promo-card {
  display: grid;
  grid-template-columns: 220px 1fr;
  gap: 28px;
  align-items: center;
  background: linear-gradient(135deg, #0f172a, #1e293b);
  color: #fff;
  border-radius: 20px;
  padding: 28px;
  box-shadow: 0 14px 34px rgba(15, 23, 42, 0.18);
}

.book-promo-cover {
  background: rgba(255, 255, 255, 0.08);
  border-radius: 16px;
  padding: 14px;
  display: flex;
  align-items: center;
  justify-content: center;
}

.book-promo-cover img {
  max-width: 100%;
  height: auto;
  display: block;
  border-radius: 8px;
}

.book-promo-label {
  display: inline-block;
  margin: 0 0 10px;
  padding: 6px 10px;
  background: #f59e0b;
  color: #111827;
  border-radius: 999px;
  font-size: 0.8rem;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.book-promo-content h3 {
  margin: 0 0 8px;
  font-size: 1.7rem;
  line-height: 1.2;
}

.book-promo-subtitle {
  margin: 0 0 14px;
  color: #cbd5e1;
  font-weight: 600;
}

.book-promo-text {
  margin: 0 0 18px;
  color: #e2e8f0;
}

.book-promo-points {
  display: flex;
  flex-wrap: wrap;
  gap: 10px 16px;
  margin-bottom: 20px;
  color: #dbeafe;
  font-size: 0.95rem;
}

.book-promo-buttons {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
}

.book-promo-buttons a {
  display: inline-block;
  text-decoration: none;
  padding: 11px 18px;
  border-radius: 10px;
  font-weight: 700;
  transition: 0.2s ease;
}

.book-promo-buttons a:first-child {
  background: #2563eb;
  color: #fff;
}

.book-promo-buttons a:first-child:hover {
  background: #1d4ed8;
}

.book-promo-buttons a:last-child {
  background: #fff;
  color: #0f172a;
}

.book-promo-buttons a:last-child:hover {
  background: #e2e8f0;
}

@media (max-width: 768px) {
  .book-promo-card {
    grid-template-columns: 1fr;
    text-align: center;
    padding: 22px;
  }

  .book-promo-cover {
    max-width: 220px;
    margin: 0 auto;
  }

  .book-promo-points,
  .book-promo-buttons {
    justify-content: center;
  }

  .book-promo-content h3 {
    font-size: 1.45rem;
  }
}

.lesson-footer {
  background: #0a0a0a;
  border-top: 1px solid var(--border);
  padding: 32px;
  text-align: center;
  font-size: 0.78rem;
  color: var(--text-dim);
}

.lesson-footer a {
  color: var(--ms-blue-light);
}

.copyright {
  margin: 8px 0;
}

.footer-bottom-links p {
  margin-top: 8px;
}

@media (max-width: 768px) {
  .nav-inner {
    padding: 0 16px;
  }

  .lesson-wrap {
    padding: 32px 16px 60px;
  }

  .book-promo-card {
    padding: 18px;
  }

  .book-promo-cover img {
    width: 150px;
  }
}