:root {
  --bg: #eef2f7;
  --panel: #ffffff;
  --text: #0f172a;
  --muted: #64748b;
  --faint: #94a3b8;
  --line: #dbe3ee;
  --line-soft: #e8edf5;
  --blue: #2563eb;
  --blue-soft: #eff6ff;
  --green: #16a34a;
  --shadow: 0 20px 60px rgba(15, 23, 42, 0.10);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
}

* {
  box-sizing: border-box;
}

html {
  min-height: 100%;
  background: var(--bg);
  color: var(--text);
}

body {
  min-height: 100%;
  margin: 0;
  background:
    linear-gradient(180deg, rgba(255, 255, 255, 0.78), rgba(238, 242, 247, 0.78)),
    var(--bg);
}

a {
  color: inherit;
  text-decoration: none;
}

.course-shell {
  min-height: 100vh;
}

.course-sidebar {
  position: fixed;
  inset: 0 auto 0 0;
  z-index: 30;
  display: flex;
  width: 292px;
  flex-direction: column;
  gap: 18px;
  padding: 18px;
  border-right: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.92);
  backdrop-filter: blur(18px);
}

.course-home-wrap {
  display: flex;
  flex-direction: column;
  margin: 8px 0 32px;
}

.course-home-card {
  position: relative;
  display: flex;
  align-items: center;
  gap: 10px;
  width: 100%;
  min-height: 44px;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: var(--panel);
  padding: 12px 16px;
  color: #334155;
  font-size: 14px;
  font-weight: 800;
  box-shadow: 0 1px 2px rgba(15, 23, 42, 0.05);
  transition: all 200ms ease;
}

.course-home-card:hover {
  border-color: #cbd5e1;
  background: #f8fafc;
  color: #334155;
  box-shadow: 0 4px 6px -1px rgba(15, 23, 42, 0.1), 0 2px 4px -2px rgba(15, 23, 42, 0.1);
}

.course-home-card__mark {
  display: grid;
  width: 24px;
  height: 24px;
  place-items: center;
  border-radius: 8px;
  background: #0f172a;
  color: #ffffff;
  font-size: 10px;
  font-weight: 950;
}

.course-home-card__label {
  white-space: nowrap;
}

.course-nav {
  display: flex;
  min-height: 0;
  flex: 1;
  flex-direction: column;
}

.course-nav__section {
  margin: 8px 8px 10px;
  color: var(--faint);
  font-size: 11px;
  font-weight: 950;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.course-nav__section--lessons {
  margin-top: 22px;
}

.course-nav__items {
  display: grid;
  gap: 8px;
}

.course-nav-link,
.course-lesson-link {
  border: 1px solid transparent;
  transition: border-color 150ms ease, background 150ms ease, color 150ms ease, transform 150ms ease;
}

.course-nav-link {
  display: grid;
  gap: 3px;
  padding: 12px 13px;
  border-radius: 15px;
  color: #334155;
  font-weight: 900;
}

.course-nav-link small {
  color: var(--muted);
  font-size: 12px;
  font-weight: 700;
}

.course-nav-link:hover,
.course-nav-link--active {
  border-color: #bfdbfe;
  background: var(--blue-soft);
  color: #1d4ed8;
}

.course-lesson-link {
  display: grid;
  grid-template-columns: 28px 1fr;
  gap: 10px;
  align-items: start;
  padding: 11px;
  border-radius: 15px;
  color: #334155;
}

.course-lesson-link span {
  display: grid;
  width: 28px;
  height: 28px;
  place-items: center;
  border-radius: 9px;
  background: #f1f5f9;
  color: var(--muted);
  font-size: 12px;
  font-weight: 950;
}

.course-lesson-link strong {
  font-size: 13px;
  line-height: 1.35;
}

.course-lesson-link:hover,
.course-lesson-link--active {
  border-color: #bbf7d0;
  background: #f0fdf4;
  color: #166534;
}

.course-sidebar__footer {
  display: flex;
  gap: 10px;
  padding-top: 14px;
  border-top: 1px solid var(--line-soft);
}

.course-sidebar__footer a {
  flex: 1;
  padding: 10px;
  border: 1px solid var(--line-soft);
  border-radius: 13px;
  background: #f8fafc;
  color: var(--muted);
  font-size: 12px;
  font-weight: 900;
  text-align: center;
}

.course-main {
  min-height: 100vh;
  padding: 20px;
}

.course-canvas {
  min-height: calc(100vh - 40px);
  margin-left: 292px;
  border: 1px solid var(--line);
  border-radius: 28px;
  background: rgba(255, 255, 255, 0.94);
  box-shadow: var(--shadow);
  overflow: hidden;
}

.course-index,
.course-overview,
.course-article {
  padding: clamp(28px, 5vw, 72px);
}

.course-index__hero,
.course-hero,
.course-article__header,
.course-prose,
.course-lesson-pager {
  max-width: 860px;
  margin: 0 auto;
}

.course-kicker {
  color: var(--blue);
  font-size: 12px;
  font-weight: 950;
  letter-spacing: 0.14em;
  text-transform: uppercase;
}

.course-index h1,
.course-hero h1,
.course-article h1 {
  margin: 12px 0 18px;
  max-width: 800px;
  font-size: clamp(40px, 5vw, 72px);
  font-weight: 950;
  letter-spacing: 0;
  line-height: 0.98;
}

.course-index p,
.course-hero p,
.course-lead {
  max-width: 720px;
  margin: 0;
  color: var(--muted);
  font-size: clamp(17px, 2vw, 21px);
  font-weight: 650;
  line-height: 1.55;
}

.course-card-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 14px;
  max-width: 980px;
  margin: 44px auto 0;
}

.course-card {
  display: grid;
  min-height: 250px;
  align-content: start;
  gap: 12px;
  padding: 24px;
  border: 1px solid var(--line-soft);
  border-radius: 22px;
  background: linear-gradient(180deg, #ffffff, #f8fafc);
  transition: border-color 150ms ease, transform 150ms ease, box-shadow 150ms ease;
}

.course-card:hover {
  border-color: #bfdbfe;
  transform: translateY(-2px);
  box-shadow: 0 16px 36px rgba(15, 23, 42, 0.10);
}

.course-card span,
.course-card em {
  color: var(--blue);
  font-size: 12px;
  font-style: normal;
  font-weight: 950;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.course-card strong {
  font-size: 25px;
  font-weight: 950;
  line-height: 1.05;
}

.course-card small {
  color: var(--muted);
  font-size: 15px;
  font-weight: 650;
  line-height: 1.55;
}

.course-card em {
  align-self: end;
  color: var(--green);
}

.course-summary-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 12px;
  max-width: 860px;
  margin: 36px auto 0;
}

.course-summary-grid div {
  padding: 18px;
  border: 1px solid var(--line-soft);
  border-radius: 18px;
  background: #f8fafc;
}

.course-summary-grid span,
.course-summary-grid strong {
  display: block;
}

.course-summary-grid span {
  color: var(--faint);
  font-size: 11px;
  font-weight: 950;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.course-summary-grid strong {
  margin-top: 7px;
  font-size: 17px;
  font-weight: 950;
  line-height: 1.25;
}

.course-lesson-list {
  display: grid;
  max-width: 860px;
  margin: 30px auto 0;
  border: 1px solid var(--line-soft);
  border-radius: 22px;
  background: #ffffff;
  overflow: hidden;
}

.course-row {
  display: grid;
  grid-template-columns: 56px 1fr;
  gap: 16px;
  padding: 20px;
  border-bottom: 1px solid var(--line-soft);
}

.course-row:last-child {
  border-bottom: none;
}

.course-row:hover {
  background: #f8fafc;
}

.course-row__number {
  display: grid;
  width: 42px;
  height: 42px;
  place-items: center;
  border-radius: 14px;
  background: var(--blue-soft);
  color: var(--blue);
  font-size: 15px;
  font-weight: 950;
}

.course-row__body strong,
.course-row__body small {
  display: block;
}

.course-row__body strong {
  font-size: 20px;
  font-weight: 950;
}

.course-row__body small {
  margin-top: 6px;
  color: var(--muted);
  font-size: 15px;
  font-weight: 650;
  line-height: 1.55;
}

.course-back-link {
  display: inline-flex;
  margin-bottom: 26px;
  color: var(--blue);
  font-size: 14px;
  font-weight: 950;
}

.course-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 8px 12px;
  margin-bottom: 14px;
  color: var(--faint);
  font-size: 13px;
  font-weight: 950;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.course-article__cover {
  margin: 30px 0 0;
}

.course-article__cover img {
  display: block;
  width: 100%;
  aspect-ratio: 16 / 9;
  object-fit: cover;
  border: 1px solid var(--line-soft);
  border-radius: 18px;
  box-shadow: 0 18px 48px rgba(15, 23, 42, 0.12);
}

.course-article__cover figcaption {
  margin-top: 10px;
  color: var(--muted);
  font-size: 13px;
  line-height: 1.5;
}

.course-prose {
  margin-top: 48px;
  color: #1e293b;
  font-size: 18px;
  line-height: 1.8;
  word-wrap: break-word;
}

.course-prose > * + * {
  margin-top: 1.5em;
}

.course-prose h2,
.course-prose h3,
.course-prose h4 {
  color: #020617;
  font-weight: 850;
  line-height: 1.2;
  letter-spacing: 0;
}

.course-prose h2 {
  margin-top: 2em;
  font-size: clamp(28px, 3.5vw, 36px);
}

.course-prose p,
.course-prose li {
  color: #334155;
}

.course-prose ul,
.course-prose ol {
  padding-left: 1.25em;
}

.course-prose li + li {
  margin-top: 0.55em;
}

.course-prose code {
  padding: 0.16em 0.34em;
  border-radius: 8px;
  background: #f1f5f9;
  color: #0f172a;
  font-size: 0.92em;
}

.course-prose img {
  display: block;
  max-width: 100%;
  height: auto;
  margin: 2.5em auto;
  border-radius: 16px;
  box-shadow: 0 10px 25px rgba(15, 23, 42, 0.08);
}

.course-lesson-pager {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
  margin-top: 46px;
}

.course-lesson-pager a {
  display: grid;
  gap: 5px;
  min-height: 92px;
  padding: 18px;
  border: 1px solid var(--line-soft);
  border-radius: 18px;
  background: #f8fafc;
}

.course-lesson-pager a:last-child {
  text-align: right;
}

.course-lesson-pager span {
  color: var(--faint);
  font-size: 12px;
  font-weight: 950;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.course-lesson-pager strong {
  font-size: 17px;
  line-height: 1.25;
}

.course-mobile-header,
.course-overlay {
  display: none;
}

@media (max-width: 1100px) {
  .course-card-grid,
  .course-summary-grid {
    grid-template-columns: 1fr;
  }

  .course-card {
    min-height: 0;
  }
}

@media (max-width: 900px) {
  .course-mobile-header {
    position: sticky;
    top: 0;
    z-index: 25;
    display: flex;
    align-items: center;
    justify-content: space-between;
    min-height: 74px;
    padding: 14px 18px;
    border-bottom: 1px solid var(--line);
    background: rgba(255, 255, 255, 0.92);
    backdrop-filter: blur(18px);
  }

  .course-mobile-title {
    margin-top: 3px;
    font-size: 18px;
    font-weight: 950;
  }

  .course-menu-button {
    display: grid;
    width: 44px;
    height: 44px;
    place-items: center;
    padding: 11px;
    border: 1px solid var(--line);
    border-radius: 14px;
    background: #ffffff;
  }

  .course-menu-button span {
    display: block;
    width: 20px;
    height: 2px;
    margin: 2px 0;
    border-radius: 99px;
    background: #0f172a;
  }

  .course-sidebar {
    width: min(86vw, 330px);
    transform: translateX(-105%);
    transition: transform 180ms ease;
  }

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

  .course-overlay {
    position: fixed;
    inset: 0;
    z-index: 20;
    border: 0;
    background: rgba(15, 23, 42, 0.38);
  }

  .course-menu-open .course-overlay {
    display: block;
  }

  .course-main {
    padding: 14px;
  }

  .course-canvas {
    min-height: calc(100vh - 102px);
    margin-left: 0;
    border-radius: 22px;
  }

  .course-index,
  .course-overview,
  .course-article {
    padding: 26px;
  }

  .course-index h1,
  .course-hero h1,
  .course-article h1 {
    font-size: 40px;
  }

  .course-lesson-pager {
    grid-template-columns: 1fr;
  }

  .course-lesson-pager a:last-child {
    text-align: left;
  }
}

@media (max-width: 520px) {
  .course-main {
    padding: 10px;
  }

  .course-canvas {
    border-radius: 18px;
  }

  .course-index,
  .course-overview,
  .course-article {
    padding: 22px;
  }

  .course-index h1,
  .course-hero h1,
  .course-article h1 {
    font-size: 34px;
  }

  .course-row {
    grid-template-columns: 42px 1fr;
    gap: 12px;
    padding: 16px;
  }
}