.chapter-mode-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 28px;
}

.chapter-mode-link,
.section-jump-link {
  min-height: 44px;
  display: inline-flex;
  align-items: center;
  padding: 9px 13px;
  border: 1px solid var(--line);
  border-radius: 10px;
  background: #fff;
  color: var(--green-dark);
  font-weight: 750;
  text-decoration: none;
}

.chapter-mode-link.current {
  border: 2px solid var(--green-dark);
  background: #eaf7f1;
  text-decoration: underline;
  text-underline-offset: 4px;
}

.chemistry-lab-subnav {
  margin-top: 14px;
  padding: 14px;
  border: 1px solid #0f5c5a;
  border-radius: 14px;
  background: #eef8f7;
}

.chemistry-lab-subnav-label {
  display: block;
  margin-bottom: 9px;
  color: #083f3e;
  font-size: .82rem;
  font-weight: 850;
  letter-spacing: .05em;
  text-transform: uppercase;
}

.chemistry-lab-links {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 10px;
}

.structure-lab-links { grid-template-columns: repeat(3, minmax(0, 1fr)); }

.chemistry-lab-link {
  min-width: 0;
  min-height: 48px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
  padding: 10px 14px;
  border: 2px solid #0f5c5a;
  border-radius: 10px;
  background: #0f5c5a;
  color: #fff;
  font-weight: 800;
  line-height: 1.25;
  text-decoration: none;
  overflow-wrap: anywhere;
}

.chemistry-lab-link:hover {
  border-color: #083f3e;
  background: #083f3e;
  color: #fff;
}

.chemistry-lab-link:focus-visible {
  outline: 3px solid #f2b84b;
  outline-offset: 3px;
}

.chemistry-lab-link.current {
  border: 3px solid #f2b84b;
  background: #083f3e;
  box-shadow: inset 5px 0 0 #fff;
}

.current-lab-marker {
  flex: 0 0 auto;
  padding: 3px 7px;
  border: 1px solid #fff;
  border-radius: 999px;
  font-size: .7rem;
  text-transform: uppercase;
  white-space: nowrap;
}

.section-jump {
  margin: 22px 0 8px;
  padding: 18px;
  border: 1px solid var(--line);
  border-radius: 14px;
  background: #f1f6f3;
}

.section-jump h3 {
  margin: 0 0 12px;
}

.section-jump-links {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.concept-group,
.conversion-section,
#worked-examples,
#interactive-labs {
  scroll-margin-top: 90px;
}

#interactive-labs .section-heading {
  flex-wrap: wrap;
  gap: 12px;
}

.lab-selection-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 18px;
}

.lab-selection-card {
  min-width: 0;
  display: flex;
  flex-direction: column;
  padding: 26px;
  border: 1px solid var(--line);
  border-radius: 18px;
  background: #fff;
  box-shadow: var(--shadow);
  overflow-wrap: anywhere;
}

.lab-selection-card h3 {
  margin: 8px -26px 16px;
  padding: 14px 26px;
  background: #0f5c5a;
  color: #fff;
  font-size: 1.45rem;
}

.lab-selection-card > p {
  color: var(--muted);
}

.lab-selection-card ul {
  padding-left: 20px;
}

.lab-selection-card .button {
  align-self: flex-start;
  margin-top: auto;
  border-color: #0f5c5a;
  background: #0f5c5a;
  color: #fff;
}

.lab-selection-card .button:hover {
  border-color: #083f3e;
  background: #083f3e;
}

.lab-selection-card .button:focus-visible {
  outline: 3px solid #f2b84b;
  outline-offset: 3px;
}

.lab-number {
  align-self: flex-start;
  padding: 4px 8px;
  border-radius: 999px;
  background: #0f5c5a;
  color: #fff;
  font-size: .78rem;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: .08em;
}

.simulation-breadcrumbs {
  display: flex;
  flex-wrap: wrap;
  gap: 10px 16px;
  margin-bottom: 20px;
}

.simulation-breadcrumbs a {
  color: var(--green-dark);
  font-weight: 700;
}

.learn-back-to-top {
  position: fixed;
  right: max(18px, calc((100vw - 1180px) / 2));
  bottom: 22px;
  z-index: 4;
  min-height: 46px;
  display: inline-flex;
  align-items: center;
  gap: 7px;
  padding: 10px 15px;
  border: 2px solid #0f5c5a;
  border-radius: 999px;
  background: #0f5c5a;
  color: #fff;
  font-weight: 800;
  text-decoration: none;
  box-shadow: 0 8px 24px rgba(7, 63, 62, .22);
}

.learn-back-to-top:hover {
  background: #083f3e;
  color: #fff;
}

.learn-back-to-top:focus-visible {
  outline: 3px solid #f2b84b;
  outline-offset: 3px;
}

.chapter-mode-link.mode-pending {
  cursor: default;
  flex-direction: column;
  gap: .15rem;
  opacity: .68;
}

.chapter-mode-link.mode-pending small {
  display: block;
  font-size: .68rem;
  font-weight: 600;
  white-space: nowrap;
}

.formula-registry,
.misconception-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(245px, 1fr));
  gap: 1rem;
}

.misconception-grid article {
  border: 1px solid var(--line, #d8e2dd);
  border-radius: 1rem;
  padding: 1.1rem;
  background: #fff;
}

@media (max-width: 760px) {
  .chapter-mode-nav {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .chapter-mode-link {
    justify-content: center;
    text-align: center;
  }

  .section-jump-links {
    flex-wrap: nowrap;
    max-width: 100%;
    overflow-x: auto;
    padding: 2px 2px 10px;
    scrollbar-width: thin;
  }

  .section-jump-link {
    flex: 0 0 auto;
  }

  .lab-selection-grid {
    grid-template-columns: 1fr;
  }

  .structure-lab-links { grid-template-columns: 1fr; }

  .lab-selection-card {
    padding: 20px;
  }

  .lab-selection-card h3 {
    margin-right: -20px;
    margin-left: -20px;
    padding-right: 20px;
    padding-left: 20px;
  }
}

@media (max-width: 540px) {
  .chemistry-lab-links {
    grid-template-columns: 1fr;
  }

  .chemistry-lab-link {
    width: 100%;
  }

  .learn-back-to-top {
    right: 12px;
    bottom: 12px;
  }
}

@media print {
  .chapter-mode-nav,
  .chemistry-lab-subnav,
  .learn-back-to-top,
  .section-jump,
  .simulation-breadcrumbs {
    display: none !important;
  }
}

.logo-brand {
  display: inline-flex;
  align-items: center;
  gap: 14px;
  font-size: 1.22rem;
  font-weight: 850;
}

.logo-brand img {
  width: 128px;
  height: 48px;
  object-fit: contain;
}

.logo-brand span {
  color: var(--ink);
}

.site-nav {
  display: flex;
  align-items: center;
  gap: 18px;
}

.site-nav a {
  min-height: 40px;
  display: inline-flex;
  align-items: center;
}

.programme-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin-top: 28px;
}

.course-panel {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 22px;
  margin-top: 42px;
  padding: 26px;
  border: 1px solid var(--line);
  border-radius: 18px;
  background: #eef7f2;
}

.course-panel h2,
.course-panel p {
  margin: 4px 0;
}

@media (max-width: 760px) {
  .site-header {
    height: auto;
    min-height: 70px;
    align-items: flex-start;
    flex-direction: column;
    gap: 8px;
    padding-top: 10px;
    padding-bottom: 10px;
  }

  .site-header .site-nav {
    display: flex;
    width: 100%;
    gap: 10px;
    overflow-x: auto;
    padding-bottom: 2px;
  }

  .logo-brand img {
    width: 108px;
    height: 40px;
  }

  .course-panel {
    align-items: flex-start;
    flex-direction: column;
  }
}

/* II PU Solid State: Unit Cell Density Explorer */
.unit-cell-lab .unit-cell-cube {
  min-height: 260px;
  display: grid;
  place-items: center;
  margin: 28px 0;
}

.unit-cell-lab .cube-face {
  width: min(280px, 72vw);
  aspect-ratio: 1;
  border: 4px solid rgba(167, 236, 227, .95);
  border-radius: 22px;
  background:
    radial-gradient(circle at 12% 12%, #a7ece3 0 12px, transparent 13px),
    radial-gradient(circle at 88% 12%, #a7ece3 0 12px, transparent 13px),
    radial-gradient(circle at 12% 88%, #a7ece3 0 12px, transparent 13px),
    radial-gradient(circle at 88% 88%, #a7ece3 0 12px, transparent 13px),
    radial-gradient(circle at 50% 50%, rgba(223,243,173,.95) 0 22px, transparent 23px),
    rgba(255,255,255,.08);
  display: grid;
  place-items: center;
  color: #fff;
  font-size: 1.5rem;
  font-weight: 900;
  text-align: center;
}

.unit-cell-lab .cube-note {
  color: #a7ece3;
  font-weight: 800;
  text-align: center;
}

.unit-cell-lab .live-readings {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
}

.unit-cell-lab .live-readings div {
  border: 1px solid rgba(167, 236, 227, .35);
  border-radius: 14px;
  padding: 14px;
  background: rgba(255,255,255,.08);
}

.unit-cell-lab .live-readings span {
  display: block;
  color: #a7ece3;
  font-size: .82rem;
}

.unit-cell-lab .live-readings strong {
  display: block;
  margin-top: 4px;
  color: #fff;
  font-size: 1.12rem;
}

/* EduProd subscriber navigation */
.site-nav .dashboard-link {
  background: #06b6d4;
  color: #083344;
  border: 1px solid #0891b2;
  border-radius: 10px;
  padding: 8px 12px;
  font-weight: 800;
}
.site-nav .dashboard-link:hover { background: #22d3ee; color: #083344; }