body.course-body {
  min-height: 100vh;
  position: relative;
}

.admin-btn {
  position: fixed;
  top: 16px;
  right: 16px;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  border: none;
  background: var(--color-surface);
  box-shadow: var(--shadow-soft);
  cursor: pointer;
  color: var(--color-subtle);
  transition: background var(--transition-fast), color var(--transition-fast);
  z-index: 1000;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 0;
}

.admin-btn .material-icons {
  font-size: 20px;
}

.admin-btn:hover {
  background: var(--color-primary);
  color: #fff;
}

.course-shell {
  max-width: 960px;
  margin: 0 auto;
  padding: 24px 20px 48px;
  display: flex;
  flex-direction: column;
  gap: 24px;
}

.course-hero h1 {
  margin: 0 0 8px 0;
  font-size: clamp(1.8rem, 4vw, 2.4rem);
}

.course-hero p {
  margin: 0;
  color: var(--color-subtle);
}

.viewer {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-soft);
  overflow: hidden;
  display: flex;
  flex-direction: column;
}

.viewer-frame {
  position: relative;
  padding-top: 56.25%;
  background: #000;
}

.viewer-frame iframe {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  border: none;
  border-radius: 0;
}

.viewer-header {
  padding: 18px 20px;
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.viewer-header h2 {
  margin: 0;
  font-size: 1.2rem;
}

.viewer-header .actions {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
}

.viewer-header .actions a {
  color: var(--color-primary);
  font-size: 0.9rem;
}

.lesson-list {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: 14px;
  counter-reset: lesson;
}

.lesson-card {
  position: relative;
  padding: 16px 16px 16px 72px;
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-soft);
  display: flex;
  gap: 16px;
  align-items: center;
  transition: transform var(--transition-fast), box-shadow var(--transition-fast);
  cursor: pointer;
}

.lesson-card::before {
  content: counter(lesson);
  counter-increment: lesson;
  position: absolute;
  left: 18px;
  top: 50%;
  transform: translateY(-50%);
  width: 40px;
  height: 40px;
  border-radius: 12px;
  background: rgba(27, 100, 242, 0.12);
  color: var(--color-primary);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 600;
  font-size: 1rem;
}

.lesson-card.active {
  box-shadow: 0 24px 40px -30px rgba(27, 100, 242, 0.8);
  transform: translateY(-2px);
  border: 1px solid rgba(27, 100, 242, 0.45);
}

.lesson-thumb {
  width: 120px;
  aspect-ratio: 16 / 9;
  border-radius: 12px;
  overflow: hidden;
  background: repeating-linear-gradient(45deg, rgba(107, 122, 153, 0.18), rgba(107, 122, 153, 0.18) 12px, rgba(107, 122, 153, 0.08) 12px, rgba(107, 122, 153, 0.08) 24px);
  flex-shrink: 0;
  position: relative;
}

.lesson-thumb img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  display: block;
}

.thumb-placeholder {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 2rem;
  color: var(--color-subtle);
}

.lesson-info {
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.lesson-info h3 {
  margin: 0;
  font-size: 1rem;
  line-height: 1.4;
}

.lesson-info .lesson-type {
  font-size: 0.8rem;
  color: var(--color-subtle);
  text-transform: uppercase;
  letter-spacing: 0.08em;
}

.empty {
  color: var(--color-subtle);
  text-align: center;
}

@media (max-width: 720px) {
  .lesson-card {
    padding: 14px 14px 14px 64px;
  }

  .lesson-thumb {
    width: 90px;
  }
}

@media (max-width: 520px) {
  .course-shell {
    padding: 16px;
  }

  .lesson-card {
    flex-direction: row;
  }

  .viewer-header {
    padding: 16px;
  }

  .viewer-header h2 {
    font-size: 1.05rem;
  }

  .viewer-header .actions {
    gap: 8px;
  }
}