/* ==================== RESET & VARS ==================== */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --bg: #0f1117;
  --bg2: #161b25;
  --bg3: #1e2535;
  --border: #2a3245;
  --text: #e8eaf0;
  --text2: #8892a4;
  --text3: #5a6478;
  --accent: #4f8ef7;
  --accent2: #7c3aed;
  --green: #22c55e;
  --yellow: #f59e0b;
  --red: #ef4444;
  --pink: #e84393;
  --sidebar-w: 240px;
}

body.light {
  --bg: #f4f6fb;
  --bg2: #ffffff;
  --bg3: #eaecf4;
  --border: #d0d5e8;
  --text: #1a1f2e;
  --text2: #4b5568;
  --text3: #9ca3af;
}

html { font-size: 15px; }
body {
  font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
  background: var(--bg);
  color: var(--text);
  display: flex;
  min-height: 100vh;
  line-height: 1.6;
  transition: background .2s, color .2s;
}

/* ==================== SIDEBAR ==================== */
#sidebar {
  width: var(--sidebar-w);
  min-width: var(--sidebar-w);
  background: var(--bg2);
  border-right: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  height: 100vh;
  position: sticky;
  top: 0;
  overflow-y: auto;
  overflow-x: hidden;
}

.sidebar-header {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 18px 16px 16px;
  border-bottom: 1px solid var(--border);
}

.logo {
  font-size: 2rem;
  color: var(--accent);
  line-height: 1;
  flex-shrink: 0;
}

.logo-title { font-weight: 700; font-size: 1rem; letter-spacing: .5px; }
.logo-sub { font-size: .72rem; color: var(--text2); }

#theme-toggle {
  margin-left: auto;
  background: none;
  border: none;
  cursor: pointer;
  font-size: 1.1rem;
  color: var(--text2);
  padding: 4px;
  border-radius: 6px;
  transition: background .15s;
}
#theme-toggle:hover { background: var(--bg3); }

.sidebar-nav { padding: 12px 8px; flex: 1; }

.nav-btn {
  display: block;
  width: 100%;
  text-align: left;
  padding: 9px 12px;
  border: none;
  background: none;
  color: var(--text2);
  border-radius: 8px;
  cursor: pointer;
  font-size: .88rem;
  margin-bottom: 2px;
  transition: background .15s, color .15s;
  font-family: inherit;
}
.nav-btn:hover { background: var(--bg3); color: var(--text); }
.nav-btn.active { background: var(--accent); color: #fff; font-weight: 600; }

.sidebar-progress {
  padding: 14px 16px;
  border-top: 1px solid var(--border);
}
.progress-label {
  display: flex;
  justify-content: space-between;
  font-size: .78rem;
  color: var(--text2);
  margin-bottom: 6px;
}
.progress-bar {
  height: 5px;
  background: var(--bg3);
  border-radius: 99px;
  overflow: hidden;
}
#progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--accent), var(--accent2));
  border-radius: 99px;
  transition: width .4s;
  width: 0%;
}

/* ==================== MAIN ==================== */
#main {
  flex: 1;
  overflow-y: auto;
  padding: 32px 40px 60px;
  min-width: 0;
}

.view { display: none; }
.view.active { display: block; animation: fadeIn .25s; }

@keyframes fadeIn { from { opacity: 0; transform: translateY(6px); } to { opacity: 1; transform: none; } }

h1 { font-size: 1.9rem; font-weight: 700; margin-bottom: 8px; }
.view-desc { color: var(--text2); margin-bottom: 28px; font-size: .95rem; }
.section-title { font-size: 1.2rem; font-weight: 600; margin: 32px 0 14px; color: var(--text); }

/* ==================== HERO ==================== */
.hero {
  background: linear-gradient(135deg, #1a237e22, #7c3aed22);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 40px 36px;
  margin-bottom: 36px;
  text-align: center;
}
.hero h1 {
  font-size: 2.6rem;
  background: linear-gradient(135deg, var(--accent), var(--accent2));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  margin-bottom: 8px;
}
.hero-sub { color: var(--text2); font-size: 1.05rem; margin-bottom: 28px; }
.hero-stats { display: flex; justify-content: center; gap: 36px; }
.stat-num { font-size: 2rem; font-weight: 800; color: var(--accent); }
.stat-label { font-size: .8rem; color: var(--text2); text-transform: uppercase; letter-spacing: 1px; }

/* ==================== ROADMAP ==================== */
.roadmap { display: flex; flex-direction: column; gap: 20px; }

.roadmap-phase {
  background: var(--bg2);
  border: 1px solid var(--border);
  border-radius: 12px;
  overflow: hidden;
}
.phase-label {
  background: var(--bg3);
  padding: 10px 18px;
  font-size: .82rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 1px;
  color: var(--text2);
  border-bottom: 1px solid var(--border);
}
.roadmap-items {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
  gap: 0;
}
.roadmap-item {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 14px 18px;
  cursor: pointer;
  text-decoration: none;
  color: var(--text);
  border-right: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
  transition: background .15s;
  font-size: .9rem;
}
.roadmap-item:hover { background: var(--bg3); color: var(--accent); }
.ri-icon {
  font-size: 1.1rem;
  width: 28px;
  height: 28px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--bg3);
  border-radius: 6px;
  flex-shrink: 0;
  font-style: normal;
}

/* ==================== QUICK ACCESS ==================== */
.quick-access {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: 12px;
}
.qa-card {
  background: var(--bg2);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 14px;
  cursor: pointer;
  transition: border-color .15s, transform .15s;
}
.qa-card:hover { border-color: var(--accent); transform: translateY(-2px); }
.qa-card-title { font-weight: 600; font-size: .88rem; margin-bottom: 4px; }
.qa-card-date { font-size: .78rem; color: var(--text2); }
.qa-card-pages { font-size: .78rem; color: var(--text3); margin-top: 6px; }
.qa-badge {
  display: inline-block;
  font-size: .7rem;
  padding: 2px 8px;
  border-radius: 99px;
  margin-bottom: 6px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: .5px;
}
.qa-badge.midterm { background: #4f8ef720; color: var(--accent); }
.qa-badge.final { background: #e8439320; color: var(--pink); }

/* ==================== EXAM GRID ==================== */
.exam-filters { display: flex; gap: 8px; margin-bottom: 22px; }
.filter-btn {
  padding: 6px 16px;
  border: 1px solid var(--border);
  background: var(--bg2);
  color: var(--text2);
  border-radius: 99px;
  cursor: pointer;
  font-size: .85rem;
  font-family: inherit;
  transition: all .15s;
}
.filter-btn.active, .filter-btn:hover { background: var(--accent); color: #fff; border-color: var(--accent); }

.exam-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 16px;
}
.exam-card {
  background: var(--bg2);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 18px;
  cursor: pointer;
  transition: border-color .15s, transform .15s;
}
.exam-card:hover { border-color: var(--accent); transform: translateY(-2px); }
.exam-card-header { display: flex; justify-content: space-between; align-items: flex-start; margin-bottom: 8px; }
.exam-card h3 { font-size: .95rem; font-weight: 600; }
.exam-card-date { font-size: .78rem; color: var(--text2); }
.exam-topics { display: flex; flex-wrap: wrap; gap: 5px; margin-top: 10px; }
.topic-tag {
  font-size: .72rem;
  padding: 2px 8px;
  border-radius: 99px;
  background: var(--bg3);
  color: var(--text2);
  border: 1px solid var(--border);
}
.exam-page-count { font-size: .78rem; color: var(--text3); margin-top: 8px; }

/* ==================== TOPIC GRID ==================== */
.topic-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 16px;
}
.topic-card {
  background: var(--bg2);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 20px;
  cursor: pointer;
  transition: border-color .15s, transform .15s;
  position: relative;
  overflow: hidden;
}
.topic-card::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 3px;
  background: var(--topic-color, var(--accent));
}
.topic-card:hover { transform: translateY(-2px); }
.topic-card-icon {
  font-size: 1.6rem;
  margin-bottom: 10px;
  display: block;
}
.topic-card h3 { font-size: 1rem; font-weight: 600; margin-bottom: 5px; }
.topic-card p { font-size: .82rem; color: var(--text2); }
.topic-card-pages { font-size: .78rem; color: var(--text3); margin-top: 10px; }

/* ==================== FORMULA SHEET ==================== */
.formula-sheet { margin-top: 24px; }
.formula-section {
  background: var(--bg2);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 24px;
  margin-bottom: 18px;
}
.formula-section h2 {
  font-size: 1.1rem;
  font-weight: 700;
  margin-bottom: 16px;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--border);
  color: var(--accent);
}
.formula-section p { margin: 10px 0; }
.formula-section ol, .formula-section ul { padding-left: 22px; margin: 10px 0; }
.formula-section li { margin: 5px 0; }
.formula { margin: 12px 0; padding: 10px 16px; background: var(--bg3); border-radius: 8px; text-align: center; overflow-x: auto; }
.theory-table {
  width: 100%;
  border-collapse: collapse;
  margin: 12px 0;
  font-size: .88rem;
}
.theory-table th, .theory-table td {
  padding: 8px 12px;
  border: 1px solid var(--border);
  text-align: left;
}
.theory-table th { background: var(--bg3); font-weight: 600; color: var(--text2); }

.btn-primary {
  background: var(--accent);
  color: #fff;
  border: none;
  padding: 9px 20px;
  border-radius: 8px;
  cursor: pointer;
  font-size: .9rem;
  font-family: inherit;
  margin-bottom: 24px;
  transition: opacity .15s;
}
.btn-primary:hover { opacity: .85; }

/* ==================== PAGE GRID ==================== */
.browse-controls {
  display: flex;
  gap: 12px;
  margin-bottom: 20px;
  flex-wrap: wrap;
}
.browse-controls input, .browse-controls select {
  padding: 8px 14px;
  background: var(--bg2);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text);
  font-size: .9rem;
  font-family: inherit;
}
.browse-controls input { flex: 1; min-width: 200px; }
.browse-controls input:focus, .browse-controls select:focus { outline: none; border-color: var(--accent); }

.page-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(160px, 1fr));
  gap: 12px;
}

.page-thumb {
  background: var(--bg2);
  border: 1px solid var(--border);
  border-radius: 10px;
  overflow: hidden;
  cursor: pointer;
  transition: border-color .15s, transform .15s;
  position: relative;
}
.page-thumb:hover { border-color: var(--accent); transform: translateY(-2px); }
.page-thumb.studied { border-color: var(--green); }
.page-thumb.bookmarked { border-color: var(--yellow); }

.page-thumb img {
  width: 100%;
  aspect-ratio: 3/4;
  object-fit: cover;
  display: block;
}
.page-thumb-info {
  padding: 6px 8px;
  font-size: .78rem;
  color: var(--text2);
  display: flex;
  justify-content: space-between;
  align-items: center;
}
.page-thumb-num { font-weight: 600; color: var(--text); }
.page-thumb-icons { display: flex; gap: 4px; font-size: .7rem; }
.thumb-badge-studied { color: var(--green); }
.thumb-badge-bookmarked { color: var(--yellow); }

/* ==================== VIEWER MODAL ==================== */
.overlay {
  position: fixed;
  inset: 0;
  background: #000c;
  z-index: 1000;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 20px;
}
.overlay.hidden { display: none; }

.viewer-modal {
  background: var(--bg2);
  border: 1px solid var(--border);
  border-radius: 14px;
  width: 100%;
  max-width: 880px;
  max-height: 96vh;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

.viewer-toolbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 12px 16px;
  border-bottom: 1px solid var(--border);
  gap: 10px;
}
.viewer-info { display: flex; align-items: center; gap: 10px; }
#viewer-page-label { font-weight: 700; font-size: 1rem; }
.viewer-exam-tag {
  font-size: .78rem;
  padding: 2px 10px;
  background: var(--bg3);
  border-radius: 99px;
  color: var(--text2);
  max-width: 300px;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}
.viewer-actions { display: flex; gap: 6px; }
.viewer-actions button {
  background: var(--bg3);
  border: 1px solid var(--border);
  color: var(--text);
  padding: 5px 11px;
  border-radius: 7px;
  cursor: pointer;
  font-size: .85rem;
  font-family: inherit;
  transition: background .15s, border-color .15s;
  white-space: nowrap;
}
.viewer-actions button:hover { background: var(--accent); border-color: var(--accent); color: #fff; }
.viewer-actions button.active { background: var(--green); border-color: var(--green); color: #fff; }

.viewer-body {
  display: flex;
  align-items: center;
  flex: 1;
  overflow: hidden;
  gap: 0;
}

.viewer-nav {
  background: none;
  border: none;
  color: var(--text2);
  font-size: 2.4rem;
  cursor: pointer;
  padding: 0 10px;
  flex-shrink: 0;
  height: 100%;
  transition: color .15s, background .15s;
  font-family: inherit;
}
.viewer-nav:hover { color: var(--accent); background: var(--bg3); }
.viewer-nav:disabled { color: var(--text3); cursor: default; }

.viewer-img-wrap {
  flex: 1;
  overflow: auto;
  display: flex;
  align-items: flex-start;
  justify-content: center;
  padding: 12px;
  max-height: calc(96vh - 160px);
}
#viewer-img {
  max-width: 100%;
  border-radius: 6px;
  transform-origin: top center;
  transition: transform .2s;
}

.viewer-notes-bar {
  border-top: 1px solid var(--border);
  padding: 10px 14px;
  display: flex;
  gap: 10px;
  align-items: flex-start;
}
#viewer-note {
  flex: 1;
  background: var(--bg3);
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: 7px;
  padding: 7px 12px;
  font-family: inherit;
  font-size: .85rem;
  resize: vertical;
}
#viewer-note:focus { outline: none; border-color: var(--accent); }
#viewer-save-note {
  background: var(--accent);
  border: none;
  color: #fff;
  padding: 7px 14px;
  border-radius: 7px;
  cursor: pointer;
  font-family: inherit;
  font-size: .85rem;
}

/* ==================== TOPIC MODAL ==================== */
.topic-modal {
  background: var(--bg2);
  border: 1px solid var(--border);
  border-radius: 14px;
  width: 100%;
  max-width: 860px;
  max-height: 90vh;
  overflow-y: auto;
  padding: 28px 32px;
  position: relative;
}
.modal-close {
  position: sticky;
  top: 0;
  float: right;
  background: var(--bg3);
  border: 1px solid var(--border);
  color: var(--text);
  width: 32px;
  height: 32px;
  border-radius: 99px;
  cursor: pointer;
  font-size: 1rem;
  font-family: inherit;
  transition: background .15s;
  margin-left: 12px;
  margin-bottom: 4px;
}
.modal-close:hover { background: var(--red); border-color: var(--red); color: #fff; }

.topic-detail-header { margin-bottom: 20px; }
.topic-detail-header h2 { font-size: 1.6rem; margin-bottom: 6px; }
.topic-detail-header p { color: var(--text2); }

.related-pages-section { margin-top: 28px; }
.related-pages-section h3 { font-size: 1.05rem; font-weight: 600; margin-bottom: 12px; }
.related-pages-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(120px, 1fr));
  gap: 8px;
}
.related-page-btn {
  background: var(--bg3);
  border: 1px solid var(--border);
  color: var(--text);
  padding: 8px;
  border-radius: 8px;
  cursor: pointer;
  font-family: inherit;
  font-size: .82rem;
  text-align: center;
  transition: all .15s;
}
.related-page-btn:hover { background: var(--accent); border-color: var(--accent); color: #fff; }

/* ==================== EMPTY STATE ==================== */
.empty-state {
  text-align: center;
  padding: 60px 20px;
  color: var(--text2);
}
.empty-icon { font-size: 3rem; margin-bottom: 14px; }

/* ==================== SCROLLBAR ==================== */
::-webkit-scrollbar { width: 6px; height: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 99px; }
::-webkit-scrollbar-thumb:hover { background: var(--text3); }

/* ==================== METU OCW BLOCK ==================== */
.metu-ocw-block {
  background: linear-gradient(135deg, #00205b12, #c8102e12);
  border: 1px solid #c8102e44;
  border-radius: 12px;
  padding: 18px 20px;
  margin-bottom: 22px;
}
.metu-ocw-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 16px;
  flex-wrap: wrap;
  gap: 10px;
}
.metu-logo-wrap { display: flex; flex-direction: column; }
.metu-logo-text {
  font-size: 1rem;
  font-weight: 800;
  letter-spacing: 1px;
  color: #c8102e;
  line-height: 1.1;
}
.metu-logo-sub { font-size: .75rem; color: var(--text2); margin-top: 1px; }
.metu-course-link {
  font-size: .8rem;
  color: #c8102e;
  text-decoration: none;
  border: 1px solid #c8102e66;
  padding: 5px 12px;
  border-radius: 6px;
  font-weight: 600;
  transition: background .15s;
}
.metu-course-link:hover { background: #c8102e18; }

.metu-section-label {
  font-size: .76rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: .8px;
  color: var(--text2);
  margin: 12px 0 6px;
}
.metu-section-label:first-of-type { margin-top: 0; }

.metu-items { display: flex; flex-direction: column; gap: 4px; }

.metu-item {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 8px 12px;
  border-radius: 7px;
  text-decoration: none;
  color: var(--text);
  font-size: .84rem;
  border: 1px solid transparent;
  transition: background .15s, border-color .15s;
}
.metu-item:hover { background: var(--bg3); border-color: var(--border); }
.metu-item.metu-video:hover { border-color: #c8102e55; background: #c8102e0c; }
.metu-item.metu-note:hover { border-color: #00205b55; background: #00205b0c; }

.metu-item-icon { font-size: .9rem; flex-shrink: 0; }
.metu-item-title { flex: 1; line-height: 1.3; }
.metu-item-arrow { font-size: .75rem; color: var(--text3); flex-shrink: 0; }
.metu-item:hover .metu-item-arrow { color: #c8102e; }

.res-section-label {
  font-size: .8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: .8px;
  color: var(--text2);
  margin: 6px 0 12px;
}

/* ==================== TOPIC DETAIL TABS ==================== */
.topic-detail-header {
  display: flex;
  align-items: flex-start;
  gap: 16px;
  margin-bottom: 24px;
  padding: 16px 20px;
  background: var(--bg3);
  border-radius: 10px;
  border-left: 4px solid var(--accent);
}
.topic-detail-icon { font-size: 2.2rem; flex-shrink: 0; line-height: 1; }
.topic-detail-header h2 { font-size: 1.5rem; margin-bottom: 4px; }
.topic-detail-header p { color: var(--text2); font-size: .9rem; }

.topic-detail-tabs {
  display: flex;
  gap: 4px;
  margin-bottom: 20px;
  background: var(--bg3);
  border-radius: 10px;
  padding: 4px;
}
.tab-btn {
  flex: 1;
  padding: 8px 14px;
  border: none;
  background: none;
  color: var(--text2);
  border-radius: 8px;
  cursor: pointer;
  font-size: .88rem;
  font-family: inherit;
  font-weight: 500;
  transition: background .15s, color .15s;
}
.tab-btn:hover { color: var(--text); background: var(--bg2); }
.tab-btn.active { background: var(--bg2); color: var(--text); box-shadow: 0 1px 4px #0003; }

.tab-panel { display: none; }
.tab-panel.active { display: block; animation: fadeIn .2s; }

.extended-theory h3 {
  font-size: 1rem;
  font-weight: 600;
  margin: 20px 0 8px;
  color: var(--accent);
}
.extended-theory h3:first-child { margin-top: 0; }
.extended-theory p { margin: 8px 0; }
.extended-theory ol, .extended-theory ul { padding-left: 22px; margin: 8px 0; }
.extended-theory li { margin: 5px 0; }

/* ==================== RESOURCES ==================== */
.resources-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
  gap: 12px;
}
.resource-card {
  display: flex;
  flex-direction: column;
  gap: 6px;
  padding: 14px 16px;
  background: var(--bg2);
  border: 1px solid var(--border);
  border-radius: 10px;
  text-decoration: none;
  color: var(--text);
  transition: border-color .15s, transform .15s, box-shadow .15s;
  cursor: pointer;
}
.resource-card:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 16px #0004;
}
.resource-card.res-video { border-top: 3px solid #ef4444; }
.resource-card.res-notes { border-top: 3px solid #4f8ef7; }
.resource-card.res-course { border-top: 3px solid #8b5cf6; }
.resource-card.res-practice { border-top: 3px solid #22c55e; }
.resource-card:hover.res-video { border-color: #ef4444; }
.resource-card:hover.res-notes { border-color: #4f8ef7; }
.resource-card:hover.res-course { border-color: #8b5cf6; }
.resource-card:hover.res-practice { border-color: #22c55e; }

.resource-card-top {
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.res-icon { font-size: 1.1rem; }
.res-badge {
  font-size: .68rem;
  padding: 2px 8px;
  border-radius: 99px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: .5px;
}
.res-badge.res-video { background: #ef444420; color: #ef4444; }
.res-badge.res-notes { background: #4f8ef720; color: #4f8ef7; }
.res-badge.res-course { background: #8b5cf620; color: #8b5cf6; }
.res-badge.res-practice { background: #22c55e20; color: #22c55e; }

.res-title {
  font-size: .88rem;
  font-weight: 600;
  line-height: 1.3;
}
.res-desc {
  font-size: .78rem;
  color: var(--text2);
  line-height: 1.4;
  flex: 1;
}
.res-link-indicator {
  font-size: .75rem;
  color: var(--text3);
  margin-top: 4px;
  align-self: flex-end;
}
.resource-card:hover .res-link-indicator { color: var(--accent); }

/* ==================== PRINT ==================== */
@media print {
  #sidebar, .viewer-modal, #viewer-overlay, #topic-overlay { display: none !important; }
  #main { padding: 0; }
  .view { display: block !important; }
  #view-formulas.view { display: block !important; }
  #view-home, #view-exams, #view-topics, #view-browse, #view-bookmarks { display: none !important; }
}

/* ==================== RESPONSIVE ==================== */
@media (max-width: 680px) {
  :root { --sidebar-w: 0px; }
  #sidebar { display: none; }
  #main { padding: 20px 16px 40px; }
  .hero h1 { font-size: 1.8rem; }
  .page-grid { grid-template-columns: repeat(auto-fill, minmax(130px, 1fr)); }
}