.lecture-applets-section {
  margin-top: 52px;
  padding-top: 34px;
  border-top: 2px solid var(--line);
}

.lecture-applets-section h2 {
  margin: 0 0 12px;
  font-size: clamp(1.7rem, 4vw, 2.5rem);
  line-height: 1.08;
}

.lecture-applet-catalog {
  display: grid;
  gap: 28px;
  margin-top: 30px;
}

.lecture-applet-group h3 {
  margin: 0 0 10px;
  color: var(--ink);
  font: 760 1.08rem/1.3 var(--sans);
}

.lecture-applet-group h3 span {
  color: var(--accent);
}

.lecture-applet-items {
  display: grid;
  gap: 10px;
}

.lecture-applet-row {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.9);
  overflow: hidden;
}

.lecture-applet-row summary {
  position: relative;
  display: flex;
  align-items: center;
  min-height: 3.7rem;
  padding: 0.75rem 3rem 0.75rem 1rem;
  cursor: pointer;
  list-style: none;
  font: 720 1rem/1.28 var(--sans);
}

.lecture-applet-row summary::-webkit-details-marker { display: none; }

.lecture-applet-row summary::after {
  content: "+";
  position: absolute;
  right: 1rem;
  color: var(--accent);
  font-size: 1.5rem;
  font-weight: 450;
}

.lecture-applet-row[open] summary::after { content: "−"; }

.lecture-applet-body {
  padding: 14px;
  border-top: 1px solid var(--line);
}

.lecture-applet-frame {
  display: block;
  width: 100%;
  aspect-ratio: 16 / 9;
  border: 1px solid var(--line-strong);
  border-radius: 6px;
  background: #111923;
}

.lecture-applet-actions {
  display: flex;
  justify-content: flex-end;
  margin-top: 10px;
}

.lecture-applet-note {
  margin-top: 12px;
  font-size: 0.94rem;
}

@media (max-width: 640px) {
  .lecture-applet-body { padding: 8px; }
  .lecture-applet-frame { min-height: 360px; aspect-ratio: auto; }
}