.problem-card {
  position: relative;
  max-width: 760px;
  margin: 0 auto;
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow-lg);
  padding: 44px 48px 48px;
  overflow: hidden;
  animation: rise 0.5s ease-out;
}

.problem-card::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 6px;
  background: linear-gradient(90deg, var(--accent), var(--accent-2), var(--accent-3));
}

.problem-header {
  display: flex;
  align-items: center;
  justify-content: flex-start;
  gap: 8px;
  margin-bottom: 14px;
}

.problem-badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  flex: none;
  white-space: nowrap;
  font-size: 0.78rem;
  font-weight: 700;
  color: #fff;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  padding: 6px 14px;
  border-radius: 999px;
  letter-spacing: 0.03em;
  box-shadow: 0 4px 10px -3px rgba(var(--accent-rgb), 0.5);
}

.problem-chapter {
  margin-left: auto;
  max-width: none;
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.03em;
  line-height: 1.3;
  text-align: center;
  white-space: nowrap;
  color: var(--accent-deep);
  background: var(--accent-soft);
  border: 1px solid var(--accent-border);
  border-radius: 999px;
  padding: 6px 12px;
}

.problem-badge svg {
  width: 13px;
  height: 13px;
}

.problem-card h1 {
  font-size: 1.4rem;
  font-weight: 800;
  letter-spacing: -0.01em;
  margin: 16px 0 0;
  color: var(--text);
}

.problem-lead {
  margin: 10px 0 0;
  font-size: 1.02rem;
  line-height: 1.55;
  color: var(--text);
}

.problem-statement {
  font-size: 1.03rem;
  color: var(--lead);
  background: var(--accent-soft);
  border: 1px solid var(--accent-border);
  border-radius: 14px;
  padding: 18px 22px;
  margin: 22px 0 30px;
}

.problem-card h2,
.method-section h2,
.result-section h2,
.verify-section h2,
.remark-section h2 {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 10px;
  font-size: 0.82rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--accent);
  margin: 32px 0 12px;
  line-height: 1.45;
}

.problem-card h2 mjx-container,
.method-section h2 mjx-container,
.result-section h2 mjx-container,
.verify-section h2 mjx-container,
.remark-section h2 mjx-container {
  text-transform: none;
  letter-spacing: normal;
}

.problem-card h2::before,
.method-section h2::before,
.result-section h2::before,
.verify-section h2::before,
.remark-section h2::before {
  content: "";
  width: 22px;
  height: 2px;
  background: var(--accent-2);
  border-radius: 2px;
}

.method-section h2 {
  color: var(--accent-deep);
}

.method-section h2::before {
  background: var(--accent-2);
}

.method-section {
  background: var(--method-bg);
  border: 1px solid var(--accent-border);
  border-radius: 14px;
  padding: 6px 22px 18px;
  margin: 22px 0 0;
}

.method-section ol {
  margin: 8px 0 4px;
  padding-left: 20px;
}

.method-section li {
  margin: 4px 0;
}

.result-section h2 {
  color: var(--green);
}

.result-section h2::before {
  background: var(--green);
}

.verify-section h2 {
  color: var(--warn);
}

.verify-section h2::before {
  background: var(--warn-bar);
}

.remark-section h2 {
  color: var(--accent-deep);
}

.remark-section h2::before {
  background: var(--accent-2);
}

.remark-section {
  background: var(--remark-bg);
  border: 1px solid var(--remark-border);
  border-radius: 14px;
  padding: 6px 22px 18px;
  margin: 22px 0 0;
}

.remark-section ul {
  margin: 8px 0 4px;
  padding-left: 20px;
}

.remark-section li {
  margin: 8px 0;
}

.result-box {
  display: block;
  width: fit-content;
  max-width: 100%;
  overflow-x: auto;
  background: var(--green-soft);
  border: 1.5px solid var(--result-border);
  border-radius: 14px;
  padding: 16px 26px;
  margin-top: 4px;
  box-shadow: var(--shadow-sm);
}

.result-box + .result-box {
  margin-left: 10px;
}

.result-row {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
}

.result-box mjx-container {
  margin: 0 !important;
}

.check {
  color: var(--green);
  font-weight: 700;
  margin-left: 6px;
}

.domain-note {
  display: inline-block;
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--accent-deep);
  background: var(--domain-bg);
  border: 1px solid var(--accent-border);
  border-radius: 999px;
  padding: 4px 12px;
  margin-top: 10px;
}

.problem-card p {
  margin: 8px 0;
}

hr.divider {
  border: none;
  border-top: 1px solid var(--border);
  margin: 30px 0 0;
}

.data-table {
  width: 100%;
  border-collapse: collapse;
  margin: 12px 0 8px;
  font-size: 0.95rem;
  overflow: hidden;
  border: 1px solid var(--border);
  border-radius: 12px;
}

.data-table th,
.data-table td {
  padding: 12px 14px;
  text-align: left;
  border-bottom: 1px solid var(--border);
}

.data-table th {
  background: var(--accent-soft);
  color: var(--accent);
  font-size: 0.78rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.data-table tbody tr:last-child td {
  border-bottom: none;
}

.data-table tbody tr:hover {
  background: var(--surface-2);
}

.case {
  background: var(--surface-2);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 12px 16px;
  margin: 12px 0;
}

.case p:first-child {
  margin-top: 0;
}

.case p:last-child {
  margin-bottom: 0;
}

.problem-card ul {
  margin: 8px 0;
  padding-left: 22px;
}

.problem-card li {
  margin: 4px 0;
}

.figure-wrap {
  margin: 16px 0 8px;
  padding: 16px;
  background: var(--surface-2);
  border: 1px solid var(--border);
  border-radius: 14px;
  overflow-x: auto;
}

.figure-caption {
  margin: 10px 0 0;
  font-size: 0.88rem;
  color: var(--muted);
  text-align: center;
}

.clause-inline {
  white-space: nowrap;
}

mjx-container[display="true"] {
  overflow-x: auto;
  max-width: 100%;
}

.problem-nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  max-width: 760px;
  margin: 0 auto;
}

.problem-nav--top {
  margin: 8px auto 18px;
}

.problem-nav--bottom {
  margin: 28px auto 0;
}

.problem-nav-btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  min-width: 118px;
  justify-content: center;
  padding: 10px 14px;
  border: 1px solid var(--border);
  border-radius: 12px;
  background: var(--card-bg);
  color: var(--text);
  font-size: 0.9rem;
  font-weight: 700;
  box-shadow: var(--shadow-sm, 0 1px 2px rgba(15, 23, 42, 0.04));
  transition: background 0.15s ease, border-color 0.15s ease, color 0.15s ease, transform 0.15s ease;
}

.problem-nav-btn:hover {
  border-color: var(--accent-border);
  color: var(--accent);
  background: var(--accent-soft);
  transform: translateY(-1px);
}

.problem-nav-btn.is-disabled {
  opacity: 0.4;
  cursor: not-allowed;
  box-shadow: none;
}

.problem-nav-meta {
  flex: 1;
  text-align: center;
  font-size: 0.88rem;
  font-weight: 700;
  color: var(--muted);
  letter-spacing: 0.01em;
}

@media (max-width: 600px) {
  .problem-card {
    padding: 30px 22px 34px;
  }

  .problem-card h1 {
    font-size: 1.2rem;
  }

  .problem-chapter {
    max-width: 58%;
    font-size: 0.68rem;
    padding: 5px 10px;
  }

  .problem-nav {
    flex-wrap: wrap;
  }

  .problem-nav-meta {
    order: -1;
    flex: 1 1 100%;
    margin-bottom: 2px;
  }

  .problem-nav-btn {
    flex: 1;
    min-width: 0;
  }
}

.problem-card h4 {
  font-size: 1.02rem;
  font-weight: 700;
  margin: 18px 0 8px;
}

.fig-grid {
  display: grid;
  gap: 18px;
  margin: 8px 0;
}

@media (min-width: 720px) {
  .fig-grid {
    grid-template-columns: 1fr 1fr;
    align-items: start;
  }
}

.fig-wrap {
  margin: 0;
  padding: 12px;
  background: #f7f5f2;
  color: #24272b;
  border-radius: 12px;
}

.fig {
  position: relative;
  container-type: inline-size;
  margin: 0 auto;
  width: 100%;
}

.fig svg {
  display: block;
  width: 100%;
  height: auto;
}

.fig .lb {
  position: absolute;
  white-space: nowrap;
  line-height: 1;
  pointer-events: none;
  font-size: calc(var(--k) * var(--s, 1) * 100cqw);
  text-shadow: 0 0 3px #fff, 0 0 3px #fff, 0 0 2px #fff;
}

.fig .lb mjx-container {
  margin: 0 !important;
}

.legend {
  list-style: none;
  margin: 10px auto 0;
  padding: 0;
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 6px 18px;
  font-size: 0.92rem;
  color: #24272b;
}

.legend li {
  display: inline-flex;
  align-items: center;
  gap: 7px;
}

.legend svg {
  flex: none;
}

.fig-wrap figcaption,
.figure-wrap figcaption {
  font-size: 0.88rem;
  color: #5b6470;
  text-align: center;
  margin-top: 8px;
  line-height: 1.5;
}

.table-wrap {
  overflow-x: auto;
  margin: 14px 0;
}

table.sum {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.95rem;
}

table.sum th,
table.sum td {
  border-bottom: 1px solid var(--border);
  padding: 8px 10px;
  text-align: left;
  vertical-align: top;
}

table.sum th {
  font-size: 0.82rem;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--muted);
}