.challenge-section { margin-top: 2rem; }
.challenge-section > h2 { font-size: 1.5rem; font-weight: 600; margin-bottom: 1rem; }
.challenge-list { display: grid; gap: 1rem; }
.challenge-card { display: flex; align-items: center; gap: 1.5rem; padding: 1.25rem; border: 1px solid var(--edge); border-radius: var(--radius); background: var(--surface); }
.challenge-featured { border-left: 3px solid var(--accent); }
.challenge-image { position: relative; flex: 0 0 12rem; width: 12rem; height: 8rem; overflow: hidden; border-radius: .4rem; background: var(--surface-2); }
.challenge-image img { width: 100%; height: 100%; object-fit: cover; }
.challenge-description { flex: 1; min-width: 0; }
.challenge-description h3 { font-size: 1.25rem; font-weight: 600; line-height: 1.2; }
.challenge-featured h3 { font-size: clamp(1.4rem, 2vw, 1.8rem); }
.challenge-description h3 a:hover { color: var(--accent); }
.challenge-deadline { color: var(--pb); font-size: .875rem; margin-bottom: .5rem; }
.challenge-combo, .challenge-date { color: var(--ink-muted); font-size: .9375rem; margin-top: .5rem; }
.challenge-personal { margin-top: .75rem; font-size: 1rem; }
.challenge-action { flex-shrink: 0; }
.challenge-history { border-top: 1px solid var(--edge); padding-top: 1rem; }
.challenge-history > summary { cursor: pointer; font-weight: 600; padding-block: .75rem; }
.challenge-history > summary span { color: var(--ink-muted); font-weight: 400; margin-left: .5rem; font-size: .875rem; }
.challenge-history .challenge-list { margin-top: .75rem; }
.challenge-empty { padding-block: 2rem; color: var(--ink-muted); }
@media (max-width: 900px) { .challenge-image { flex-basis: 8rem; width: 8rem; height: 7rem; } }
@media (max-width: 640px) {
  .challenge-card { flex-wrap: wrap; gap: 1rem; }
  .challenge-image { flex-basis: 4.5rem; width: 4.5rem; height: 4.5rem; align-self: flex-start; }
  .challenge-action { width: 100%; }
  .challenge-description { flex-basis: calc(100% - 5.5rem); }
}