.chapter04-page .equation-card {
  min-width: 0;
  margin: 1rem 0;
  padding: 0;
  overflow-x: auto;
  border: 0;
  border-radius: 0;
  background: transparent;
  box-shadow: none;
}

.chapter04-page .equation-card mjx-container,
.chapter04-page .chapter-claim mjx-container,
.chapter04-page .derivation-formula mjx-container {
  max-width: 100%;
  overflow-x: auto;
  overflow-y: hidden;
}

.chapter04-page .chapter-claim {
  margin: 1.45rem 0 1.2rem;
  padding: 1rem 0;
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  color: var(--ink);
  font-weight: 800;
  text-align: center;
}

.chapter04-page .derivation-block {
  margin: 1.45rem 0 1.65rem;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: var(--radius-md);
  background: var(--paper);
  box-shadow: none;
}

.chapter04-page .derivation-step {
  display: grid;
  grid-template-columns: minmax(0, 1.15fr) minmax(14rem, .85fr);
  gap: 1rem;
  align-items: center;
  padding: 1rem 1.1rem;
  border-bottom: 1px solid var(--line);
  background: transparent;
}

.chapter04-page .derivation-step:last-child {
  border-bottom: 0;
}

.chapter04-page .derivation-formula {
  min-width: 0;
  color: var(--ink);
  font-weight: 800;
}

.chapter04-page .derivation-formula mjx-container[display="true"] {
  margin: .3em 0 !important;
}

.chapter04-page .derivation-note {
  min-width: 0;
  margin: 0;
  padding-left: 1rem;
  border-left: 1px solid var(--blue-line);
  color: var(--body);
  line-height: 1.72;
}

.chapter04-page .derivation-note > :first-child {
  margin-top: 0;
}

.chapter04-page .derivation-note > :last-child {
  margin-bottom: 0;
}

.chapter04-page .derivation-step.is-result .derivation-formula {
  color: var(--blue-deep);
}

.chapter04-page .article-list {
  display: grid;
  gap: .55rem;
  margin: 1.15rem 0 1.4rem;
  padding-left: 1.35rem;
  color: var(--body);
}

.chapter04-page .decision-path {
  display: grid;
  gap: .75rem;
  margin: 1.15rem 0 1.4rem;
  padding-left: 1.6rem;
  color: var(--body);
}

.chapter04-page .decision-path li {
  padding-left: .3rem;
}

.chapter04-page .decision-path li::marker {
  color: var(--blue-deep);
  font-weight: 900;
}

.chapter04-page .learning-lines {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0;
  margin: 1rem 0;
}

.chapter04-page .learning-lines > div {
  display: grid;
  min-width: 0;
  gap: .45rem;
  padding: .2rem 1rem;
  border-left: 1px solid var(--line);
  background: transparent;
}

.chapter04-page .learning-lines > div:first-child {
  padding-left: 0;
  border-left: 0;
}

.chapter04-index .learning-lines strong {
  color: var(--ink);
}

.chapter04-page .learning-lines span {
  margin: 0;
  color: var(--muted);
}

.chapter04-index .chapter04-lesson-list {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: .8rem;
  margin: 1.3rem 0;
}

.chapter04-index .chapter04-lesson-card {
  display: grid;
  min-width: 0;
  min-height: 202px;
  gap: .65rem;
  padding: 1rem;
  align-content: start;
  border: 1px solid var(--line);
  border-top: 3px solid var(--blue);
  border-radius: var(--radius-md);
  background: var(--paper);
  box-shadow: var(--soft-shadow);
  text-decoration: none;
  transition: border-color .18s ease, transform .18s ease;
}

.chapter04-index .chapter04-lesson-card:hover,
.chapter04-index .chapter04-lesson-card:focus-visible {
  border-color: var(--blue-line);
  outline: 0;
  transform: translateY(-2px);
}

.chapter04-index .lesson-tag {
  display: inline-flex;
  width: max-content;
  padding: .2rem .55rem;
  border-radius: var(--radius-pill);
  background: var(--blue-soft);
  color: var(--blue-deep);
  font-size: .72rem;
  font-weight: 900;
}

.chapter04-index .chapter04-lesson-card strong {
  display: block;
  color: var(--ink);
  font-size: 1.07rem;
  line-height: 1.45;
}

.chapter04-index .chapter04-lesson-card p {
  margin: 0;
  color: var(--body);
  font-size: .92rem;
}

.chapter04-index .lesson-formula {
  display: grid;
  min-height: 44px;
  margin-top: auto;
  padding: .55rem;
  place-items: center;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: .82rem;
  font-weight: 800;
}

.chapter04-page #summary .marker,
.chapter04-page #summary h2.marker {
  border-left-color: var(--cyan);
  background: transparent;
  color: var(--cyan-deep);
}

.chapter04-page #summary .marker span {
  border-color: var(--cyan-line);
  color: var(--cyan-deep);
  box-shadow: none;
}

.chapter04-page #summary .summary-panel {
  padding: 1.35rem 1.4rem;
  border: 0;
  border-left: 2px solid var(--cyan);
  border-radius: 0;
  background: var(--cyan-soft);
  box-shadow: none;
}

.chapter04-page #summary .summary-panel::after {
  display: none;
}

.chapter04-page #summary .summary-formula {
  padding: 0 0 .85rem;
  border: 0;
}

.chapter04-page #summary .summary-formula + .summary-formula {
  margin-top: .85rem;
  padding-top: .85rem;
  border-top: 1px solid var(--cyan-line);
}

@media (max-width: 820px) {
  .chapter04-page .derivation-step {
    grid-template-columns: minmax(0, 1fr);
    gap: .65rem;
    padding: .9rem;
  }

  .chapter04-page .derivation-note {
    padding-top: .65rem;
    padding-left: 0;
    border-top: 1px solid var(--line);
    border-left: 0;
  }

  .chapter04-page .learning-lines {
    grid-template-columns: minmax(0, 1fr);
  }

  .chapter04-page .learning-lines > div,
  .chapter04-page .learning-lines > div:first-child {
    padding: .85rem 0;
    border-top: 1px solid var(--line);
    border-left: 0;
  }

  .chapter04-page .learning-lines > div:first-child {
    border-top: 0;
  }

  .chapter04-index .chapter04-lesson-list {
    grid-template-columns: minmax(0, 1fr);
  }

  .chapter04-index .chapter04-lesson-card {
    min-height: 0;
  }
}

@media (max-width: 640px) {
  .chapter04-page .equation-card,
  .chapter04-page .chapter-claim {
    width: 100%;
  }

  .chapter04-page .chapter-claim {
    padding: .85rem 0;
  }

  .chapter04-page .derivation-block {
    margin: 1.2rem 0 1.4rem;
    border-radius: var(--radius-sm);
  }

  .chapter04-page #summary .summary-panel {
    padding: 1.1rem 1rem;
  }

  .chapter04-page mjx-container[display="true"] {
    font-size: 94% !important;
  }
}

@media print {
  .chapter04-page .derivation-block {
    break-inside: avoid;
  }
}