.stem-shell {
  width: min(100%, 1580px);
  margin: 0 auto;
  padding: 2.4rem clamp(1rem, 2.2vw, 2rem) 3rem;
}

.stem-hero {
  margin-bottom: 1.15rem;
}

.stem-hero h1 {
  margin: 0.32rem 0 0.58rem;
  font-size: clamp(2rem, 4.2vw, 3.2rem);
}

.stem-subtitle {
  margin: 0;
  color: #c4d2eb;
  max-width: 78ch;
  line-height: 1.5;
}

.stem-subject-grid {
  display: grid;
  gap: 1rem;
}

.subject-card {
  border: 1px solid rgba(255, 255, 255, 0.16);
  border-radius: 16px;
  background: rgba(19, 24, 32, 0.88);
  overflow: hidden;
}

.subject-card > summary {
  list-style: none;
  cursor: pointer;
  padding: 1rem 1rem 0.92rem;
  background: linear-gradient(
    130deg,
    rgba(34, 43, 58, 0.96),
    rgba(20, 27, 35, 0.94)
  );
  border-bottom: 1px solid rgba(255, 255, 255, 0.12);
}

.subject-card > summary::-webkit-details-marker {
  display: none;
}

.subject-summary {
  display: grid;
  gap: 0.26rem;
}

.subject-summary > span:first-child {
  font-family: "Orbitron", sans-serif;
  letter-spacing: 0.05em;
  font-size: clamp(1.05rem, 2vw, 1.32rem);
  color: #f7fbff;
}

.subject-kicker {
  color: #9fd8ff;
  font-size: 0.84rem;
  letter-spacing: 0.04em;
}

.subject-intro {
  padding: 0.95rem 1rem 0.4rem;
  color: #d5e1f8;
  line-height: 1.46;
}

.branch-grid {
  padding: 0.35rem 1rem 1rem;
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.75rem;
}

.branch-card {
  border: 1px solid rgba(255, 255, 255, 0.14);
  border-radius: 14px;
  background: linear-gradient(
    160deg,
    rgba(18, 25, 34, 0.98),
    rgba(13, 19, 25, 0.98)
  );
  overflow: hidden;
}

.branch-card > summary {
  list-style: none;
  cursor: pointer;
  display: grid;
  grid-template-columns: 92px 1fr;
  gap: 0.72rem;
  align-items: center;
  padding: 0.72rem;
}

.branch-card > summary::-webkit-details-marker {
  display: none;
}

.branch-summary img {
  width: 92px;
  height: 72px;
  object-fit: cover;
  border-radius: 10px;
  border: 1px solid rgba(255, 255, 255, 0.18);
  box-shadow: 0 0 14px rgba(84, 215, 255, 0.2);
}

.branch-summary span {
  font-family: "Orbitron", sans-serif;
  font-size: 0.93rem;
  color: #f3f8ff;
  letter-spacing: 0.035em;
}

.branch-body {
  border-top: 1px solid rgba(255, 255, 255, 0.1);
  padding: 0.75rem 0.72rem 0.82rem;
}

.branch-body p {
  margin: 0 0 0.62rem;
  color: #d2def3;
  line-height: 1.45;
  font-size: 0.92rem;
}

.refined-grid {
  display: grid;
  gap: 0.55rem;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  margin-bottom: 0.65rem;
}

.refined-grid article {
  border: 1px solid rgba(255, 255, 255, 0.14);
  border-radius: 10px;
  padding: 0.56rem;
  background: linear-gradient(
    160deg,
    rgba(36, 19, 22, 0.34),
    rgba(18, 30, 37, 0.44)
  );
}

.refined-grid h4 {
  margin: 0;
  font-size: 0.78rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: #ffd59f;
}

.refined-grid p {
  margin: 0.36rem 0 0;
  font-size: 0.82rem;
  color: #d5e2f8;
  line-height: 1.38;
}

.term-list {
  margin: 0;
  padding-left: 1rem;
  display: grid;
  gap: 0.34rem;
}

.term-list li {
  color: #d6e4fb;
  font-size: 0.86rem;
  line-height: 1.4;
}

.term-list strong {
  color: #9ee6ff;
}

.subject-card[open],
.branch-card[open] {
  box-shadow:
    0 0 0 1px rgba(255, 255, 255, 0.05) inset,
    0 0 24px rgba(83, 213, 255, 0.14);
}

.subject-card > summary:hover,
.subject-card > summary:focus-visible,
.branch-card > summary:hover,
.branch-card > summary:focus-visible {
  filter: brightness(1.05);
}

.stem-reference-library {
  margin-top: 1.2rem;
  border: 1px solid rgba(255, 255, 255, 0.16);
  border-radius: 16px;
  padding: 1rem;
  background: rgba(16, 22, 30, 0.9);
}

.library-head h2 {
  margin: 0;
  font-family: "Orbitron", sans-serif;
  letter-spacing: 0.05em;
  font-size: clamp(1.1rem, 2.2vw, 1.5rem);
  color: #eff8ff;
}

.library-head p {
  margin: 0.6rem 0 0;
  color: #d2def4;
  line-height: 1.5;
}

.reference-grid {
  margin-top: 0.85rem;
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.72rem;
}

.reference-topic {
  border: 1px solid rgba(255, 255, 255, 0.14);
  border-radius: 12px;
  padding: 0.68rem 0.7rem;
  background: linear-gradient(
    160deg,
    rgba(20, 29, 39, 0.96),
    rgba(14, 20, 28, 0.98)
  );
}

.reference-topic h3 {
  margin: 0;
  font-size: 0.88rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: #ffd59c;
}

.reference-topic p {
  margin: 0.42rem 0 0.58rem;
  color: #d7e3f8;
  line-height: 1.42;
  font-size: 0.86rem;
}

.reference-topic ul {
  margin: 0;
  padding-left: 1rem;
  display: grid;
  gap: 0.32rem;
}

.reference-topic li {
  color: #d6e6fe;
  font-size: 0.84rem;
  line-height: 1.38;
}

.reference-topic strong {
  color: #93e8ff;
}

@media (max-width: 1100px) {
  .branch-grid {
    grid-template-columns: 1fr;
  }

  .refined-grid {
    grid-template-columns: 1fr 1fr;
  }

  .reference-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 640px) {
  .stem-shell {
    padding: 1.2rem 0.62rem 2rem;
  }

  .subject-card,
  .branch-card {
    border-radius: 12px;
  }

  .branch-card > summary {
    grid-template-columns: 1fr;
  }

  .branch-summary img {
    width: 100%;
    height: 156px;
  }

  .refined-grid {
    grid-template-columns: 1fr;
  }
}