.arena-page {
  display: flex;
  flex-direction: column;
  gap: 20px;
}

.arena-header {
  align-items: flex-start;
  gap: 16px;
}

.arena-source-note {
  min-width: 260px;
  padding: 14px 16px;
  border: 1px solid var(--border);
  border-radius: 16px;
  background: linear-gradient(180deg, rgb(var(--well-rgb) / calc(0.04 * var(--well-k))), rgb(var(--well-rgb) / calc(0.01 * var(--well-k))));
}

.arena-stage-card {
  display: flex;
  align-items: center;
  gap: 14px;
  padding: 16px 18px;
}

.arena-stage-badge {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 80px;
  padding: 8px 12px;
  border-radius: 999px;
  background: var(--accent);
  color: var(--on-accent);
  font-size: 0.8rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.arena-stage-copy {
  color: var(--text);
  line-height: 1.6;
}

.arena-layout {
  display: grid;
  grid-template-columns: minmax(280px, 360px) minmax(0, 1fr);
  gap: 20px;
  align-items: start;
}

.arena-sidebar,
.arena-detail {
  min-height: 640px;
}

.arena-sidebar {
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.arena-sidebar-header {
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.arena-filter-row {
  display: flex;
}

.arena-filter-label {
  display: block;
  margin-bottom: 6px;
  font-size: 0.88rem;
  font-weight: 600;
  color: var(--text);
}

.arena-problem-list {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.arena-problem-card {
  width: 100%;
  padding: 14px;
  border: 1px solid var(--border);
  border-radius: 16px;
  background: var(--surface);
  text-align: left;
  cursor: pointer;
  transition: border-color 0.16s ease, box-shadow 0.16s ease, transform 0.16s ease;
}

.arena-problem-card:hover,
.arena-problem-card:focus-visible {
  border-color: var(--info);
  box-shadow: 0 10px 24px var(--shadow-soft);
  transform: translateY(-1px);
  outline: none;
}

.arena-problem-card.active {
  border-color: var(--info);
  box-shadow: 0 12px 30px var(--shadow-soft);
  background: linear-gradient(180deg, color-mix(in srgb, var(--info) 8%, var(--surface)), var(--surface));
}

.arena-problem-card-title {
  font-size: 1rem;
  font-weight: 700;
  color: var(--white);
}

.arena-problem-card-meta {
  margin-top: 8px;
  font-size: 0.83rem;
  color: var(--muted);
}

.arena-problem-card-summary {
  margin-top: 10px;
  font-size: 0.92rem;
  line-height: 1.5;
  color: var(--text);
}

.arena-detail {
  display: flex;
  flex-direction: column;
  gap: 18px;
}

.arena-detail-empty {
  display: grid;
  place-items: center;
  min-height: 420px;
  color: var(--muted);
  text-align: center;
  font-size: 1.02rem;
}

.arena-detail-header {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  align-items: flex-start;
}

.arena-detail-title-block {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.arena-chapter-pill {
  display: inline-flex;
  width: fit-content;
  padding: 6px 10px;
  border-radius: 999px;
  background: rgb(var(--info-rgb) / 0.12);
  color: var(--info);
  font-size: 0.76rem;
  font-weight: 700;
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

.arena-problem-id {
  color: var(--muted);
  font-size: 0.92rem;
}

.arena-readiness {
  min-width: 220px;
  padding: 14px 16px;
  border: 1px solid var(--border);
  border-radius: 16px;
  background: var(--surface-2);
}

.arena-readiness-label {
  font-size: 0.8rem;
  font-weight: 700;
  letter-spacing: 0.05em;
  text-transform: uppercase;
  color: var(--muted);
}

.arena-readiness-value {
  margin-top: 6px;
  font-size: 1.45rem;
  font-weight: 700;
  color: var(--white);
}

.arena-readiness-note {
  margin-top: 6px;
  font-size: 0.88rem;
  line-height: 1.5;
  color: var(--text);
}

.arena-section {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.arena-section-title {
  font-size: 0.95rem;
  font-weight: 700;
  color: var(--white);
}

.arena-summary {
  font-size: 1rem;
  line-height: 1.7;
  color: var(--text);
}

.arena-chip-row {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.arena-chip {
  display: inline-flex;
  align-items: center;
  padding: 8px 12px;
  border-radius: 999px;
  background: rgb(var(--accent-2-rgb) / 0.12);
  color: var(--accent-2);
  font-size: 0.86rem;
  font-weight: 600;
}

.arena-skill-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 12px;
}

.arena-exercise-list {
  margin: 0;
  padding-left: 0;
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 6px;
  font-size: 0.92rem;
  line-height: 1.5;
  color: var(--text);
}

.arena-exercise-list li {
  display: grid;
  grid-template-columns: 56px minmax(0, 1fr) auto;
  align-items: center;
  gap: 10px;
}

.arena-exercise-id {
  font-variant-numeric: tabular-nums;
  font-size: 0.78rem;
  font-weight: 700;
  color: var(--muted);
  letter-spacing: 0.02em;
}

.arena-exercise-link {
  color: var(--accent-2);
  text-decoration: none;
  border-bottom: 1px dashed rgb(var(--accent-2-rgb) / 0.35);
}

.arena-exercise-link:hover {
  color: var(--white);
  border-bottom-style: solid;
}

.arena-exercise-readiness {
  display: inline-flex;
  align-items: center;
  padding: 3px 10px;
  border-radius: 999px;
  font-size: 0.78rem;
  font-weight: 700;
  font-variant-numeric: tabular-nums;
  background: rgb(var(--tint-rgb) / calc(0.1 * var(--tint-k)));
  color: var(--text);
}

.arena-exercise-readiness--ready { background: rgb(var(--ok-rgb) / 0.16); color: var(--ok); }
.arena-exercise-readiness--borderline { background: rgb(var(--warn-rgb) / 0.16); color: var(--warn); }
.arena-exercise-readiness--partial { background: rgb(var(--warn-rgb) / 0.3); color: var(--warn); }
.arena-exercise-readiness--needs-prereq { background: rgb(var(--danger-rgb) / 0.16); color: var(--danger); }

.arena-exercise-empty {
  font-size: 0.88rem;
  color: var(--muted);
  font-style: italic;
}

.arena-skill-card {
  padding: 14px;
  border: 1px solid var(--border);
  border-radius: 14px;
  background: var(--surface);
}

.arena-skill-name {
  font-weight: 700;
  color: var(--white);
}

.arena-skill-weight {
  margin-top: 8px;
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--info);
}

.arena-skill-note {
  margin-top: 4px;
  font-size: 0.82rem;
  color: var(--muted);
}

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

.arena-secondary-link {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 10px 14px;
  border-radius: 12px;
  border: 1px solid var(--border);
  color: var(--white);
  text-decoration: none;
  font-weight: 600;
  background: var(--surface);
}

.arena-metadata-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 14px;
}

.arena-metadata-card {
  padding: 14px;
  border: 1px solid var(--border);
  border-radius: 14px;
  background: var(--surface-2);
}

.arena-metadata-label {
  font-size: 0.8rem;
  font-weight: 700;
  letter-spacing: 0.05em;
  text-transform: uppercase;
  color: var(--muted);
}

.arena-metadata-value {
  margin-top: 8px;
  color: var(--white);
  word-break: break-word;
  line-height: 1.5;
}

@media (max-width: 980px) {
  .arena-layout {
    grid-template-columns: 1fr;
  }

  .arena-detail-header {
    flex-direction: column;
  }

  .arena-readiness {
    min-width: 0;
    width: 100%;
  }
}