/* Calm stats strip */
    .problems-stats-row {
      display: flex;
      justify-content: space-between;
      align-items: center;
      gap: 0.8rem;
      flex-wrap: wrap;
      margin: 0.9rem 0 0.2rem;
    }

    .problem-stats-pill {
      display: flex;
      gap: 1.2rem;
      background: var(--card);
      padding: 0.55rem 0.85rem;
      border-radius: 999px;
      border: 1px solid var(--border-soft);
      box-shadow: var(--shadow-soft);
      font-size: 0.78rem;
    }

    .problem-stats-pill > div {
      display: flex;
      flex-direction: column;
      align-items: flex-start;
    }

    .problem-stats-pill strong {
      font-size: 0.95rem;
      color: var(--text-main);
      line-height: 1.15;
    }

    .problem-stats-pill span {
      color: var(--text-soft);
    }

    .stats-note {
      font-size: 0.8rem;
      color: var(--text-soft);
      max-width: 36rem;
    }

    @media (max-width: 720px) {
      .problem-stats-pill {
        width: 100%;
        justify-content: space-between;
      }
    }

    /* Quiet poster byline */
    .prob-byline {
      margin-top: 0.28rem;
      font-size: 0.82rem;
      color: var(--text-soft);
      line-height: 1.25;
      max-width: 100%;
      white-space: normal;
      display: flex;
      gap: 0.45rem;
      flex-wrap: wrap;
      align-items: center;
    }

    .prob-card-reward .prob-byline {
      margin-top: -0.6rem;
      margin-bottom: 0.5rem;
    }

    .prob-byline strong {
      color: var(--text-main);
      font-weight: 700;
      white-space: normal;
      word-break: normal;
      overflow-wrap: normal;
    }

    .prob-byline:empty {
      display: none;
    }

    .prob-media {
      margin: 0.45rem 0 0.7rem;
      border: 1px solid var(--border-soft);
      border-radius: 0.95rem;
      overflow: hidden;
      background: rgba(148, 163, 184, 0.04);
      max-width: 620px;
    }

    .prob-media-frame {
      position: relative;
      padding-top: 56.25%;
      background: #000;
    }

    .prob-media iframe,
    .prob-media video {
      display: block;
      width: 100%;
      border: 0;
      background: #000;
    }

    .prob-media-frame iframe {
      position: absolute;
      inset: 0;
      height: 100%;
    }

    .badge-reward {
      color: #0f172a;
      background: linear-gradient(135deg, rgba(251, 191, 36, 0.22), rgba(34, 197, 94, 0.16));
      border: 1px solid rgba(251, 191, 36, 0.38);
    }

    .prob-tag-reward {
      border: 1px solid rgba(251, 191, 36, 0.38);
      background: rgba(251, 191, 36, 0.12);
      color: var(--text-main);
      font-weight: 800;
    }

    /* =========================================================
       ✅ IMPROVED TAGS
       ========================================================= */
    .prob-tag-surface {
      display: inline-flex;
      align-items: center;
      justify-content: center;
      gap: 0.4rem;
      padding: 0.34rem 0.82rem;
      min-height: 2rem;
      border-radius: 999px;
      font-size: 0.74rem;
      font-weight: 800;
      letter-spacing: 0.01em;
      line-height: 1;
      white-space: nowrap;
      vertical-align: middle;
      box-sizing: border-box;
      position: relative;
      top: -5px;
    }

    .prob-tag-community {
      border: 1px solid rgba(22, 101, 52, 0.14);
      background: #eaf8ef;
      color: #166534;
      box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.65);
    }

    .prob-tag-community::before {
      content: "";
      width: 0.42rem;
      height: 0.42rem;
      border-radius: 50%;
      background: #22c55e;
      flex: 0 0 auto;
    }

    body.theme-dark .prob-tag-community {
      color: #d1fae5;
      border-color: rgba(74, 222, 128, 0.22);
      background: rgba(34, 197, 94, 0.14);
      box-shadow: none;
    }

    body.theme-dark .prob-tag-community::before {
      background: #4ade80;
    }

    .prob-tag-company {
      border: 1px solid rgba(59, 130, 246, 0.22);
      background: linear-gradient(135deg, rgba(59, 130, 246, 0.10), rgba(14, 165, 233, 0.08));
      color: #1d4ed8;
    }

    body.theme-dark .prob-tag-company {
      color: #bfdbfe;
      border-color: rgba(96, 165, 250, 0.24);
    }

    .prob-tags,
    .thread-tags {
      display: flex;
      flex-wrap: wrap;
      gap: 0.5rem;
      margin: 0.72rem 0 0.58rem;
      align-items: center;
    }

    .prob-card .prob-tag-community,
    .prob-card .prob-tag-company,
    .prob-card .prob-tag-reward {
      margin-bottom: 0.12rem;
    }

    .challenge-note-card {
      margin-top: 1rem;
      border: 1px solid rgba(34, 197, 94, 0.18);
      border-radius: 1rem;
      padding: 0.95rem 1rem;
      background:
        radial-gradient(circle at top right, rgba(251, 191, 36, 0.10), transparent 35%),
        linear-gradient(135deg, rgba(34, 197, 94, 0.10), rgba(56, 189, 248, 0.06));
    }

    .challenge-note-card strong {
      display: block;
      margin-bottom: 0.28rem;
      color: var(--text-main);
      font-size: 0.95rem;
    }

    .challenge-note-card span {
      color: var(--text-soft);
      line-height: 1.5;
      font-size: 0.9rem;
    }

    .hall-note-card {
      margin-top: 1rem;
      border: 1px solid rgba(245, 158, 11, 0.26);
      border-radius: 1rem;
      padding: 1rem 1.05rem;
      background:
        radial-gradient(circle at top left, rgba(245, 158, 11, 0.18), transparent 34%),
        radial-gradient(circle at top right, rgba(14, 165, 233, 0.14), transparent 36%),
        linear-gradient(135deg, rgba(255, 247, 237, 0.92), rgba(255, 255, 255, 0.92));
      box-shadow: 0 16px 40px rgba(245, 158, 11, 0.10);
    }

    body.theme-dark .hall-note-card {
      background:
        radial-gradient(circle at top left, rgba(245, 158, 11, 0.18), transparent 34%),
        radial-gradient(circle at top right, rgba(14, 165, 233, 0.14), transparent 36%),
        linear-gradient(135deg, rgba(30, 41, 59, 0.88), rgba(15, 23, 42, 0.92));
    }

    .hall-note-card strong {
      display: block;
      margin-bottom: 0.32rem;
      color: var(--text-main);
      font-size: 0.97rem;
      letter-spacing: 0.01em;
    }

    .hall-note-card span {
      color: var(--text-soft);
      line-height: 1.55;
      font-size: 0.91rem;
    }

    .hall-sidebar-block {
      border-color: rgba(245, 158, 11, 0.24);
      background:
        radial-gradient(circle at top left, rgba(245, 158, 11, 0.10), transparent 34%),
        radial-gradient(circle at top right, rgba(14, 165, 233, 0.08), transparent 36%),
        linear-gradient(135deg, rgba(255, 250, 240, 0.92), rgba(255, 255, 255, 0.92));
    }

    body.theme-dark .hall-sidebar-block {
      background:
        radial-gradient(circle at top left, rgba(245, 158, 11, 0.14), transparent 34%),
        radial-gradient(circle at top right, rgba(14, 165, 233, 0.10), transparent 36%),
        linear-gradient(135deg, rgba(30, 41, 59, 0.88), rgba(15, 23, 42, 0.92));
    }

    .hall-sidebar-block h2 {
      color: var(--text-main);
    }

    /* Long-title + LaTeX-safe title area */
    .prob-title {
      overflow-wrap: break-word;
      word-break: normal;
      hyphens: none;
    }

    .prob-title mjx-container[jax="SVG"] {
      display: inline-block;
      max-width: 100%;
      overflow-x: auto;
      overflow-y: hidden;
      vertical-align: middle;
      -webkit-overflow-scrolling: touch;
    }

    .prob-title mjx-container[jax="SVG"] svg {
      max-width: 100%;
      height: auto;
    }

    .prob-card-header {
      display: grid;
      grid-template-columns: minmax(0, 1fr) auto;
      align-items: start;
      gap: 0.55rem 1rem;
    }

    .prob-title,
    .prob-byline {
      grid-column: 1;
    }

    .prob-meta-top {
      grid-column: 2;
      grid-row: 1 / span 2;
      align-self: start;
      justify-self: end;
      display: inline-flex;
      align-items: center;
      gap: 0.55rem;
      white-space: nowrap;
    }

    .prob-date {
      font-size: 0.8rem;
      color: var(--text-soft);
      white-space: nowrap;
    }

    .problem-layout.problems-list-page {
      grid-template-columns: minmax(0, 1fr) 320px;
      gap: 1.2rem;
    }

    @media (max-width: 900px) {
      .problem-layout.problems-list-page {
        grid-template-columns: minmax(0, 1fr);
        gap: 1rem;
      }
    }

    @media (max-width: 720px) {
      .prob-card-header {
        grid-template-columns: minmax(0, 1fr);
      }

      .prob-meta-top {
        grid-column: 1;
        grid-row: auto;
        justify-self: start;
        white-space: normal;
      }
    }

    /* MathJax safety */
    .prob-card {
      overflow: hidden;
    }

    .prob-card mjx-container[jax="SVG"] {
      max-width: 100%;
      overflow-x: auto;
      overflow-y: hidden;
      -webkit-overflow-scrolling: touch;
    }

    .prob-card mjx-container[jax="SVG"][display="true"] {
      display: block;
      padding-bottom: 0.25rem;
    }

    .prob-card mjx-container[jax="SVG"] svg {
      max-width: 100%;
      height: auto;
    }

    /* Tabs */
    .problem-tabs-shell {
      margin-top: 0.95rem;
      display: grid;
      gap: 0.75rem;
    }

    .problem-tabs-container {
      overflow-x: auto;
      -webkit-overflow-scrolling: touch;
      min-height: 3.25rem;
      scrollbar-width: none;
      -ms-overflow-style: none;
    }

    .problem-tabs-container::-webkit-scrollbar {
      display: none;
    }

    .problem-tabs {
      display: flex;
      flex-wrap: nowrap;
      gap: 0.6rem;
      min-width: max-content;
      padding-bottom: 0.35rem;
    }

    .problem-tabs-primary {
      min-width: 0;
      padding-bottom: 0;
      gap: 0.75rem;
    }

    .problem-tabs-primary .tab-btn {
      font-size: 1rem;
      font-weight: 800;
      color: var(--text-soft);
      padding: 0.15rem 0.1rem 0.35rem;
      border-radius: 0;
      border: none;
      border-bottom: 2px solid transparent;
      background: transparent;
    }

    .problem-tabs-primary .tab-btn.active {
      color: var(--text-main);
      border-bottom-color: rgba(34, 197, 94, 0.82);
    }

    .problem-tabs-primary .tab-btn[data-group="hall"].active {
      border-bottom-color: rgba(245, 158, 11, 0.82);
    }

    .problem-subtabs {
      display: none;
      align-items: center;
    }

    .problem-subtabs.active {
      display: flex;
    }

    .problem-subtabs .tab-btn {
      font-weight: 700;
    }

    .problem-tabs .tab-btn {
      white-space: nowrap;
      flex: 0 0 auto;
    }

    /* Toolbar mobile */
    @media (max-width: 720px) {
      .problem-toolbar-modern {
        display: grid;
        grid-template-columns: 1fr;
        gap: 0.65rem;
        align-items: stretch;
      }

      .search-container,
      .sort-container {
        width: 100%;
        min-width: 0;
      }

      .search-input-wrapper,
      #problem-search-input,
      .sort-select-modern {
        width: 100%;
        min-width: 0;
      }

      .sort-container {
        display: grid;
        grid-template-columns: auto 1fr;
        gap: 0.6rem;
        align-items: center;
      }

      .sort-label-text {
        white-space: nowrap;
      }
    }

    /* Cards never overflow */
    #problems-list,
    .prob-card,
    .prob-card * {
      min-width: 0;
    }

    /* Math teaser */
    .prob-math-teaser {
      margin-top: 0.6rem;
      font-size: 0.95rem;
      opacity: 0.95;
      overflow: hidden;
    }

    /* Loading UX */
    #problems-list {
      min-height: 0;
    }

    #problems-list:has(.prob-skeleton) {
      min-height: 520px;
    }

    /* Results meta */
    .results-head {
      margin: 0.7rem 0 0.6rem;
    }

    .results-meta {
      color: var(--text-soft);
      font-size: 0.85rem;
      line-height: 1.3;
    }

    .chip-row {
      display: flex;
      gap: 0.45rem;
      flex-wrap: wrap;
      margin-top: 0.5rem;
      align-items: center;
    }

    .filter-chip {
      display: inline-flex;
      align-items: center;
      gap: 0.35rem;
      border-radius: 999px;
      border: 1px solid var(--border-soft);
      background: rgba(148, 163, 184, 0.08);
      color: var(--text-main);
      padding: 0.28rem 0.65rem;
      font-size: 0.78rem;
      font-weight: 800;
      cursor: pointer;
      user-select: none;
      transition: transform .12s ease, border-color .12s ease, background .12s ease;
      white-space: nowrap;
    }

    .filter-chip:hover {
      transform: translateY(-1px);
      border-color: rgba(56, 189, 248, 0.45);
      background: rgba(56, 189, 248, 0.10);
    }

    .filter-chip .x {
      font-weight: 900;
      opacity: 0.85;
    }

    .filter-chip.clear {
      border-color: rgba(239, 68, 68, 0.35);
      background: rgba(239, 68, 68, 0.06);
      color: var(--text-main);
    }

    .filter-chip.clear:hover {
      border-color: rgba(239, 68, 68, 0.65);
      background: rgba(239, 68, 68, 0.10);
    }

    .list-footer {
      margin: 1rem 0 0.5rem;
      display: flex;
      gap: 0.6rem;
      flex-wrap: wrap;
      align-items: center;
    }

    .mini-note {
      font-size: 0.8rem;
      color: var(--text-soft);
      opacity: 0.95;
    }

    .pagination {
      display: flex;
      gap: 0.45rem;
      flex-wrap: wrap;
      align-items: center;
    }

    .page-btn {
      border-radius: 999px;
      border: 1px solid var(--border-soft);
      background: var(--card);
      color: var(--text-main);
      padding: 0.42rem 0.78rem;
      font-size: 0.82rem;
      font-weight: 850;
      cursor: pointer;
      transition: transform .12s ease, border-color .12s ease, background .12s ease;
      user-select: none;
      white-space: nowrap;
    }

    .page-btn:hover {
      transform: translateY(-1px);
      border-color: rgba(56, 189, 248, 0.55);
      background: rgba(56, 189, 248, 0.08);
    }

    .page-btn:disabled {
      opacity: 0.55;
      cursor: not-allowed;
      transform: none;
    }

    .page-btn.active {
      border-color: rgba(34, 197, 94, 0.65);
      background: rgba(34, 197, 94, 0.10);
    }

    .prob-tag-hall {
      border: 1px solid rgba(245, 158, 11, 0.34);
      background: linear-gradient(135deg, rgba(245, 158, 11, 0.16), rgba(14, 165, 233, 0.10));
      color: #92400e;
      box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.6);
    }

    body.theme-dark .prob-tag-hall {
      color: #fde68a;
      border-color: rgba(245, 158, 11, 0.32);
      box-shadow: none;
    }

    .prob-card-hall {
      border-color: rgba(245, 158, 11, 0.22);
      box-shadow:
        0 18px 44px rgba(245, 158, 11, 0.08),
        0 0 0 1px rgba(245, 158, 11, 0.06) inset;
      background:
        radial-gradient(circle at top right, rgba(245, 158, 11, 0.10), transparent 28%),
        var(--card);
    }

    .prob-card-hall-answer {
      background:
        radial-gradient(circle at top left, rgba(14, 165, 233, 0.09), transparent 28%),
        radial-gradient(circle at top right, rgba(245, 158, 11, 0.10), transparent 30%),
        var(--card);
    }

    .badge-hall-answer {
      color: #0f172a;
      border: 1px solid rgba(14, 165, 233, 0.30);
      background: linear-gradient(135deg, rgba(125, 211, 252, 0.34), rgba(245, 158, 11, 0.18));
    }

    body.theme-dark .badge-hall-answer {
      color: #e0f2fe;
    }

    .prob-hall-note {
      margin: 0.75rem 0 0.85rem;
      padding: 0.82rem 0.92rem;
      border-radius: 0.95rem;
      border: 1px solid rgba(245, 158, 11, 0.20);
      background: rgba(255, 247, 237, 0.78);
    }

    body.theme-dark .prob-hall-note {
      background: rgba(30, 41, 59, 0.56);
    }

    .prob-hall-note-head {
      display: flex;
      justify-content: space-between;
      gap: 0.65rem;
      align-items: baseline;
      flex-wrap: wrap;
      margin-bottom: 0.35rem;
    }

    .prob-hall-kicker {
      font-size: 0.72rem;
      font-weight: 900;
      letter-spacing: 0.08em;
      text-transform: uppercase;
      color: #b45309;
    }

    body.theme-dark .prob-hall-kicker {
      color: #fbbf24;
    }

    .prob-hall-meta {
      font-size: 0.76rem;
      color: var(--text-soft);
    }

    .prob-hall-note p {
      margin: 0;
      color: var(--text-main);
      line-height: 1.55;
      font-size: 0.9rem;
    }

    .page-ellipsis {
      padding: 0.42rem 0.25rem;
      font-weight: 900;
      color: var(--text-soft);
      user-select: none;
    }

    .pagination.pagination-rail {
      flex-wrap: nowrap;
      overflow: hidden;
      align-items: center;
      gap: 0.45rem;
      width: 100%;
    }

    .pagination .pager-cluster {
      display: inline-flex;
      align-items: center;
      gap: 0.45rem;
      flex: 0 0 auto;
    }

    .pagination .pager-strip {
      display: flex;
      align-items: center;
      gap: 0.45rem;
      flex: 1 1 auto;
      overflow-x: auto;
      overflow-y: hidden;
      scroll-behavior: smooth;
      -webkit-overflow-scrolling: touch;
      padding: 0.15rem 0.2rem;
      scrollbar-width: none;
      overscroll-behavior-x: contain;
      scroll-snap-type: x proximity;
    }

    .pagination .pager-strip::-webkit-scrollbar {
      display: none;
    }

    .pagination .pager-strip .page-btn,
    .pagination .pager-strip .page-ellipsis {
      flex: 0 0 auto;
      scroll-snap-align: center;
    }

    @media (hover: hover) and (pointer: fine) {
      .pagination .pager-strip {
        cursor: grab;
      }

      .pagination .pager-strip.is-dragging {
        cursor: grabbing;
      }
    }

    .pagination .pager-jump {
      display: inline-flex;
      align-items: center;
      gap: 0.35rem;
      flex: 0 0 auto;
      white-space: nowrap;
    }

    @media (max-width: 720px) {
      .pagination.pagination-rail {
        flex-wrap: wrap;
        overflow: visible;
        gap: 0.55rem;
      }

      .pagination .pager-cluster {
        flex: 1 1 auto;
        justify-content: space-between;
        width: calc(50% - 0.3rem);
      }

      .pagination .pager-strip {
        order: 3;
        width: 100%;
        flex: 0 0 100%;
        padding: 0.25rem 0.15rem;
      }

      .pagination .pager-jump {
        order: 4;
        width: 100%;
        justify-content: flex-end;
        gap: 0.45rem;
      }

      .page-btn {
        padding: 0.38rem 0.65rem;
        font-size: 0.8rem;
      }

      .pagination .pager-jump input[type="number"] {
        width: 4.6rem !important;
      }
    }

    #results-head,
    #problems-list {
      scroll-margin-top: 96px;
    }

    @media (max-width: 720px) {
      #results-head,
      #problems-list {
        scroll-margin-top: 88px;
      }
    }

    .prob-card.focus-flash {
      outline: 3px solid rgba(59, 130, 246, 0.55);
      outline-offset: 2px;
      box-shadow: 0 0 0 6px rgba(59, 130, 246, 0.12);
      transition: box-shadow 900ms ease, outline-color 900ms ease;
      animation: focusFlashFade 1.6s ease forwards;
    }

    @keyframes focusFlashFade {
      0% {
        outline-color: rgba(59, 130, 246, 0.55);
        box-shadow: 0 0 0 6px rgba(59, 130, 246, 0.12);
      }

      100% {
        outline-color: rgba(59, 130, 246, 0);
        box-shadow: 0 0 0 0 rgba(59, 130, 246, 0);
      }
    }

    .prob-card:focus,
    .prob-card:focus-visible,
    .prob-card:focus-within {
      outline: none !important;
      box-shadow: none;
    }