@layer layout {
  .skip-link {
    position: absolute;
    left: 1rem;
    top: -4rem;
    z-index: 100;
    padding: 0.75rem 1rem;
    border-radius: var(--radius-full);
    background: var(--color-primary-dark);
    color: var(--color-text-inverted);
    transition: top var(--transition-fast);
  }

  .skip-link:focus {
    top: 1rem;
  }

  .course-shell {
    width: min(1280px, calc(100vw - 32px));
    margin: 0 auto;
    padding: 1.5rem 0 3.5rem;
  }

  .course-header {
    display: grid;
    gap: 1.5rem;
    padding: clamp(1.5rem, 3vw, 2.25rem);
    border: 1px solid rgba(216, 210, 197, 0.36);
    border-radius: var(--radius-xl);
    background:
      linear-gradient(
        135deg,
        rgba(4, 26, 35, 0.94),
        rgba(9, 56, 74, 0.9) 58%,
        rgba(20, 88, 104, 0.92)
      ),
      linear-gradient(
        0deg,
        rgba(255, 255, 255, 0.06),
        rgba(255, 255, 255, 0.06)
      );
    color: var(--color-text-inverted);
    box-shadow: var(--shadow-lg);
  }

  .course-header__grid {
    display: grid;
    grid-template-columns: minmax(0, 1.25fr) minmax(280px, 0.75fr);
    gap: 1.5rem;
    align-items: end;
  }

  .course-header__section {
    margin-bottom: 0.5rem;
    color: rgba(215, 237, 242, 0.82);
    font-size: var(--font-size-sm);
    font-weight: var(--font-weight-semibold);
    letter-spacing: 0.08em;
    text-transform: uppercase;
  }

  .course-header__title {
    max-width: 14ch;
    font-size: clamp(2rem, 1.3rem + 2vw, 3.5rem);
    font-weight: var(--font-weight-bold);
    line-height: 0.95;
  }

  .course-header__summary {
    max-width: 58ch;
    margin-top: 1rem;
    color: rgba(248, 250, 252, 0.82);
    font-size: var(--font-size-md);
  }

  .course-header__signals {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 0.9rem;
  }

  .course-signal-card {
    padding: 1rem;
    border: 1px solid rgba(255, 255, 255, 0.12);
    border-radius: var(--radius-lg);
    background: rgba(255, 255, 255, 0.07);
    box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.08);
  }

  .course-signal-card__label {
    color: rgba(215, 237, 242, 0.74);
    font-size: 0.78rem;
    font-weight: var(--font-weight-semibold);
    letter-spacing: 0.08em;
    text-transform: uppercase;
  }

  .course-signal-card__value {
    margin-top: 0.35rem;
    font-size: 1rem;
    font-weight: var(--font-weight-semibold);
    line-height: 1.35;
  }

  .course-nav {
    position: sticky;
    top: 1rem;
    z-index: 20;
    display: grid;
    grid-template-columns: minmax(0, 1fr) minmax(300px, 360px);
    gap: 1rem;
    align-items: center;
    margin-top: 1rem;
    padding: 0.85rem;
    border: 1px solid var(--glass-border);
    border-radius: var(--radius-xl);
    background: var(--glass-bg);
    backdrop-filter: var(--glass-blur);
    box-shadow: var(--shadow-sm);
  }

  .course-nav__links {
    display: flex;
    flex-wrap: wrap;
    gap: 0.65rem;
  }

  .course-search-strip {
    margin-top: 1rem;
  }

  .course-main-shell {
    display: grid;
    grid-template-columns: minmax(0, 1fr);
    gap: 1.5rem;
    margin-top: 1.5rem;
  }

  .course-main {
    min-width: 0;
  }

  .course-footer {
    margin-top: 2rem;
    padding: 1.3rem 1.5rem;
    border: 1px solid rgba(216, 210, 197, 0.48);
    border-radius: var(--radius-xl);
    background: rgba(255, 253, 248, 0.74);
    box-shadow: var(--shadow-xs);
    color: var(--color-text-muted);
  }

  .course-footer__grid {
    display: grid;
    grid-template-columns: minmax(0, 1fr) auto;
    gap: 1rem;
    align-items: center;
  }

  .course-footer__links {
    display: flex;
    flex-wrap: wrap;
    gap: 1rem;
  }

  @media (max-width: 900px) {
    .course-shell {
      width: min(100vw - 20px, 100%);
      padding-top: 0.75rem;
    }

    .course-header__grid,
    .course-nav,
    .course-footer__grid {
      grid-template-columns: 1fr;
    }

    .course-header__title {
      max-width: none;
    }

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

  @media (max-width: 640px) {
    .course-shell {
      width: min(100vw - 16px, 100%);
    }

    .course-header,
    .course-nav,
    .course-footer {
      border-radius: var(--radius-lg);
    }

    .course-header__signals,
    .course-nav__links {
      grid-template-columns: 1fr;
    }

    .course-nav__links,
    .course-footer__links {
      gap: 0.55rem;
    }
  }
}