/* Keep the paper library close to its search, on every screen. */
@media (max-width: 1050px) {
  .study-strip-inner { grid-template-columns: minmax(0, 1fr); gap: 4px; }
  .exam-countdown { grid-template-columns: max-content minmax(0, 1fr) max-content; }
  .library-update { max-width: 100%; }
  .hero-grid { gap: var(--space-8); }
  .hero-aside { padding: 20px; }
  .paper-card { grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); gap: var(--space-4); }
  .resources-grid { gap: var(--space-3); }
  .resource-block { padding-left: var(--space-3); }
  .resource-actions { gap: 2px; }
  .about-grid { gap: var(--space-8); }
  .viewer-panel-header { flex-direction: column; align-items: flex-start; }
}
@media (max-width: 760px) {
  .container { width: calc(100% - 36px); }
  .site-header { position: static; }
  .header-inner { flex-wrap: wrap; gap: var(--space-2); min-height: 0; padding-top: var(--space-3); }
  .brand { min-height: 44px; font-size: 1rem; }
  .brand-mark { width: 39px; height: 39px; }
  .site-nav { width: 100%; justify-content: space-between; gap: var(--space-1); padding-bottom: var(--space-1); }
  .site-nav a { min-height: 44px; padding: 10px var(--space-3); font-size: .85rem; white-space: nowrap; }
  .nav-indicator { bottom: var(--space-1); }
  .study-strip-inner { gap: 4px; padding-block: 10px; }
  .exam-countdown { grid-template-columns: minmax(0, 1fr); grid-template-rows: 18px 18px 28px; row-gap: 3px; }
  .exam-source { width: fit-content; }
  .library-update { max-width: 100%; font-size: .7rem; }
  .hero { padding-block: 26px; }
  .hero-grid { grid-template-columns: 1fr; gap: var(--space-6); }
  .hero h1 { font-size: clamp(2rem, 6vw, 2.7rem); }
  .hero-aside { padding: 12px 14px 8px; border-left: 3px solid var(--amber); }
  .hero-aside .mini-label, .hero-study-title, .math-figure { display: none; }
  .study-steps { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 8px; }
  .study-steps > div { border: 0; padding: 0; gap: 4px; flex-direction: column; align-items: flex-start; }
  .study-steps .icon { display: none; }
  .study-steps p { font-size: .72rem; line-height: 1.4; }
  .study-steps > div:last-child { border: 0; }
  .study-channel { margin-top: 6px; }
  .section { padding-block: var(--space-6); }
  .paper-card { grid-template-columns: 1fr; gap: var(--space-4); padding: 20px var(--space-3); }
  .resources-grid { gap: 18px; }
  .resource-block { padding: 0; border-left: 0; }
  .resource-actions { gap: var(--space-1) var(--space-2); }
  .purpose-inner, .footer-inner { flex-direction: column; align-items: flex-start; }
  .purpose-inner h2 { font-size: 1.6rem; }
  .footer-inner { padding-block: 26px 20px; }
  .footer-links { width: min(370px, 100%); gap: 0 20px; }
  .archive-intro { padding: var(--space-6) 0; }
  .archive-section { padding: 20px 0 44px; }
  .filters-card { padding: 0 0 var(--space-6); }
  input[type="search"], .filter-field select { font-size: var(--text-base); }
  .viewer-section { padding: 20px 0 44px; }
  .viewer-content { padding: var(--space-4); }
  .video-layout { grid-template-columns: 1fr; }
  .video-list { max-height: none; }
  .video-player-block { grid-row: 1; }
  .about-intro { padding: var(--space-8) 0; }
  .about-grid { grid-template-columns: 1fr; gap: var(--space-6); }
  .about-side { min-height: 190px; }
  .about-feature-grid { grid-template-columns: 1fr; }
  .youtube-cta { align-items: flex-start; flex-direction: column; }
  .not-found-section { padding-block: var(--space-12); }
}
@media (max-width: 480px) {
  .container { width: calc(100% - 28px); }
  .brand-name small { font-size: .6rem; }
  .site-nav a { padding-inline: 10px; }
  .hero h1 { margin: var(--space-3) 0; font-size: clamp(1.65rem, 6vw, 2rem); }
  .hero-eyebrow { font-size: .65rem; letter-spacing: .07em; }
  .hero-subtitle { font-size: .92rem; }
  .hero-search { gap: 6px; padding: 5px 5px 5px 10px; }
  .hero-search > .icon { width: 18px; height: 18px; }
  .hero-search input { min-height: 44px; width: 0; }
  .hero-search .btn { min-height: 44px; padding-inline: var(--space-3); font-size: .82rem; }
  .hero-search .btn .icon { display: none; }
  .hero-helper { font-size: .75rem; }
  .subject-shortcuts { column-gap: var(--space-3); margin-top: 6px; }
  .subject-shortcuts > span { flex-basis: 100%; }
  .subject-shortcuts a { font-size: .76rem; }
  .section-top { align-items: flex-start; flex-direction: column; gap: 6px; }
  .year-list { gap: var(--space-2); }
  .year-chip { min-width: 64px; padding-inline: 10px; }
  .paper-title { font-size: 1.04rem; }
  .paper-card { padding-inline: var(--space-2); }
  .resources-grid { grid-template-columns: 1fr; gap: var(--space-2); }
  .resource-block { flex-direction: row; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: var(--space-1) var(--space-2); border-top: 1px solid var(--border-light); padding-top: var(--space-2); }
  .resource-heading { font-size: .78rem; }
  .resource-actions { gap: var(--space-1); }
  .action-link { font-size: .78rem; padding-inline: 6px; }
  .filter-field { flex-basis: calc(50% - var(--space-2)); min-width: 0; }
  .filters-row { gap: var(--space-3); }
  .reset-button { width: 100%; border: 1px solid var(--border); background: var(--surface); }
  .sort-label { display: none; }
  .viewer-heading h1 { font-size: 1.8rem; }
  .viewer-tab { font-size: .8rem; padding: 10px var(--space-3); }
  .viewer-actions { width: 100%; }
  .viewer-actions .btn { flex: 1 1 170px; }
  .pdf-frame { height: 65vh; min-height: 400px; }
  .viewer-content { padding: var(--space-3); }
  .footer-bottom { flex-direction: column; gap: var(--space-1); }
  .about-intro h1 { font-size: 2.1rem; }
  .section-end .btn { width: 100%; }
}