/* DSA Venn Explorer — production-ready design system */

:root {
  --surface-0: #080d18;
  --surface-1: #0f172a;
  --surface-2: #1e293b;
  --surface-3: #273449;

  --bg-app: radial-gradient(ellipse 120% 80% at 50% -20%, rgba(99, 102, 241, 0.12), transparent 50%),
            linear-gradient(180deg, var(--surface-0) 0%, var(--surface-1) 100%);
  --bg-card: rgba(30, 41, 59, 0.72);
  --bg-card-hover: rgba(39, 52, 73, 0.9);
  --bg-inset: rgba(8, 13, 24, 0.45);
  --border-subtle: rgba(255, 255, 255, 0.06);
  --border-card: rgba(255, 255, 255, 0.1);
  --border-strong: rgba(255, 255, 255, 0.16);

  --text-primary: #f1f5f9;
  --text-secondary: #94a3b8;
  --text-muted: #64748b;

  --accent: #818cf8;
  --accent-strong: #a5b4fc;
  --accent-muted: rgba(129, 140, 248, 0.14);
  --accent-border: rgba(129, 140, 248, 0.35);

  --color-blind75: #a78bfa;
  --color-grind75: #38bdf8;
  --color-leetcode150: #4ade80;
  --color-neetcode150: #fbbf24;

  --easy: #34d399;
  --easy-bg: rgba(52, 211, 153, 0.14);
  --medium: #fbbf24;
  --medium-bg: rgba(251, 191, 36, 0.14);
  --hard: #f87171;
  --hard-bg: rgba(248, 113, 113, 0.14);
  --solved: #38bdf8;

  --font-title: 'Outfit', system-ui, sans-serif;
  --font-body: 'Plus Jakarta Sans', system-ui, sans-serif;

  --fs-xs: 0.8125rem;
  --fs-sm: 0.875rem;
  --fs-base: 0.9375rem;
  --fs-md: 1rem;
  --fs-lg: 1.125rem;
  --fs-xl: 1.375rem;

  --gap: 1rem;
  --radius-sm: 8px;
  --radius: 12px;
  --radius-lg: 16px;

  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.25);
  --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.28);
  --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.35);

  --transition: 0.18s ease;
  --content-max: 1720px;
}

*, *::before, *::after { margin: 0; padding: 0; box-sizing: border-box; }

html {
  color-scheme: dark;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-body);
  font-size: var(--fs-base);
  background: var(--surface-0);
  background-image: var(--bg-app);
  background-attachment: fixed;
  color: var(--text-primary);
  min-height: 100vh;
  padding: 1.25rem 1.5rem 2rem;
  line-height: 1.55;
  overflow-x: hidden;
  overflow-y: auto;
}

.app-container {
  max-width: var(--content-max);
  margin: 0 auto;
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
}

.sr-only {
  position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px;
  overflow: hidden; clip: rect(0,0,0,0); white-space: nowrap; border: 0;
}

/* ── Header ── */
.app-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1.25rem;
  padding: 0.85rem 1.1rem;
  background: var(--bg-card);
  border: 1px solid var(--border-card);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  flex-shrink: 0;
}

.header-brand {
  display: flex;
  align-items: center;
  gap: 0.85rem;
  min-width: 0;
}

.brand-mark {
  width: 42px;
  height: 42px;
  border-radius: 11px;
  background: var(--accent-muted);
  border: 1px solid var(--accent-border);
  color: var(--accent-strong);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.brand-mark svg { width: 22px; height: 22px; }

.header-left { min-width: 0; }

#main-title {
  font-family: var(--font-title);
  font-size: var(--fs-xl);
  font-weight: 700;
  line-height: 1.2;
  letter-spacing: -0.02em;
  color: var(--text-primary);
}

.subtitle {
  color: var(--text-muted);
  font-size: var(--fs-sm);
  margin-top: 0.2rem;
}

.subtitle-link {
  color: var(--accent);
  text-decoration: none;
  transition: color var(--transition);
}

.subtitle-link:hover {
  color: var(--accent-strong);
  text-decoration: underline;
}

.header-nav {
  display: flex;
  align-items: center;
  gap: 0.45rem;
  flex-shrink: 0;
}

.header-nav-link {
  display: inline-flex;
  align-items: center;
  padding: 0.35rem 0.7rem;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-subtle);
  background: var(--bg-inset);
  color: var(--text-secondary);
  font-size: var(--fs-xs);
  font-weight: 600;
  text-decoration: none;
  transition: border-color var(--transition), color var(--transition), background var(--transition);
}

.header-nav-link:hover {
  color: var(--accent-strong);
  border-color: var(--accent-border);
  background: var(--accent-muted);
}

.header-stats {
  display: flex;
  gap: 0.5rem;
  flex-shrink: 0;
}

.stat-pill {
  display: flex;
  flex-direction: column;
  align-items: center;
  background: var(--bg-inset);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-sm);
  padding: 0.45rem 0.85rem;
  min-width: 68px;
  transition: border-color var(--transition), background var(--transition);
}

.stat-pill:hover { background: rgba(255,255,255,0.04); }

.stat-pill.total { border-bottom: 2px solid var(--color-blind75); }
.stat-pill.common { border-bottom: 2px solid var(--color-grind75); }
.stat-pill.unique { border-bottom: 2px solid var(--color-neetcode150); }
.stat-pill.solved { border-bottom: 2px solid var(--solved); }

.stat-val {
  font-family: var(--font-title);
  font-size: var(--fs-lg);
  font-weight: 700;
  line-height: 1;
  color: var(--text-primary);
}

.stat-lbl {
  font-size: var(--fs-xs);
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.04em;
  margin-top: 3px;
  font-weight: 600;
}

/* ── Cards & layout ── */
.card {
  background: var(--bg-card);
  border: 1px solid var(--border-card);
  border-radius: var(--radius-lg);
  padding: 1rem;
  backdrop-filter: blur(12px);
  box-shadow: var(--shadow-md);
}

.main-workspace {
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
}

.venn-section,
.questions-section {
  min-width: 0;
}

.panel-heading {
  padding: 0.75rem 1rem 0;
  flex-shrink: 0;
}

.panel-title {
  font-family: var(--font-title);
  font-size: var(--fs-md);
  font-weight: 600;
  color: var(--text-primary);
  letter-spacing: -0.01em;
}

.panel-subtitle {
  font-size: var(--fs-sm);
  color: var(--text-muted);
  margin-top: 0.15rem;
}

/* ── Venn panel ── */
.venn-card {
  padding: 0 !important;
  display: flex;
  flex-direction: column;
  min-height: 0;
}

.venn-hint {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.75rem;
  margin: 0.5rem 1rem 0;
  padding: 0.5rem 0.7rem;
  background: var(--accent-muted);
  border: 1px solid var(--accent-border);
  border-radius: var(--radius-sm);
  font-size: var(--fs-sm);
  color: var(--accent-strong);
  flex-shrink: 0;
}

.venn-hint[hidden] { display: none !important; }

.venn-hint-dismiss {
  background: none;
  border: none;
  color: var(--text-muted);
  font-size: 1.25rem;
  line-height: 1;
  cursor: pointer;
  padding: 0 0.15rem;
  transition: color var(--transition);
}

.venn-hint-dismiss:hover { color: var(--text-primary); }

/* Venn diagram + controls side by side */
.venn-explorer-body {
  display: grid;
  grid-template-columns: minmax(0, 1.15fr) minmax(280px, 1fr);
  gap: 0;
  align-items: stretch;
  border-top: 1px solid var(--border-subtle);
}

.venn-stage {
  min-width: 0;
  display: flex;
  flex-direction: column;
  justify-content: center;
  background: radial-gradient(ellipse 90% 65% at 50% 38%, rgba(99, 102, 241, 0.07), transparent 68%),
    rgba(8, 13, 24, 0.35);
  border-right: 1px solid var(--border-subtle);
}

.venn-wrapper {
  position: relative;
  width: 100%;
  aspect-ratio: 1;
  max-height: 420px;
  margin: 0.5rem auto;
  padding: 0.5rem;
  line-height: 0;
  background: var(--bg-inset);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius);
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.03);
}

#venn-svg {
  width: 100%;
  height: 100%;
  display: block;
  overflow: visible;
  border-radius: calc(var(--radius) - 4px);
}

.venn-legend {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 0.5rem 1rem;
  padding: 0.4rem 0.75rem 0.65rem;
  border-top: 1px solid var(--border-subtle);
}

/* Controls panel beside diagram */
.venn-controls-panel {
  min-width: 0;
  overflow-y: auto;
  padding: 0.65rem 1rem 0.85rem;
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
  align-self: stretch;
}

.venn-controls-panel::-webkit-scrollbar { width: 6px; }
.venn-controls-panel::-webkit-scrollbar-thumb {
  background: rgba(255,255,255,0.12);
  border-radius: 3px;
}

.sources-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 0.45rem;
  flex-shrink: 0;
}

.source-card {
  background: var(--bg-inset);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-sm);
  padding: 0.5rem 0.6rem;
  cursor: pointer;
  transition: border-color var(--transition), background var(--transition), box-shadow var(--transition), opacity var(--transition);
  position: relative;
  border-left: 3px solid transparent;
}

.source-card.blind75 { border-left-color: var(--color-blind75); }
.source-card.grind75 { border-left-color: var(--color-grind75); }
.source-card.leetcode150 { border-left-color: var(--color-leetcode150); }
.source-card.neetcode150 { border-left-color: var(--color-neetcode150); }

.source-card:hover {
  background: var(--bg-card-hover);
  border-color: var(--border-card);
  box-shadow: var(--shadow-sm);
}

.source-card.selected-card {
  background: rgba(56, 189, 248, 0.12);
  border-color: rgba(56, 189, 248, 0.45);
  box-shadow: 0 0 0 1px rgba(56, 189, 248, 0.35);
}

.source-card.active-card {
  background: var(--accent-muted);
  border-color: var(--accent-border);
  box-shadow: 0 0 0 1px var(--accent-border);
}

.source-card.selected-card.active-card {
  background: var(--accent-muted);
  border-color: var(--accent-strong);
  box-shadow: 0 0 0 2px var(--accent-border);
}

.source-card-inner {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 0.65rem;
}

.source-count {
  font-family: var(--font-title);
  font-size: var(--fs-md);
  font-weight: 700;
  flex-shrink: 0;
  margin-top: 2px;
}

.source-name-row {
  display: flex;
  align-items: center;
  gap: 0.45rem;
}

.source-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  flex-shrink: 0;
}

.source-info h3 {
  font-family: var(--font-title);
  font-size: var(--fs-sm);
  font-weight: 600;
  line-height: 1.3;
  color: var(--text-primary);
}

.source-meta {
  font-size: var(--fs-xs);
  color: var(--text-muted);
  line-height: 1.4;
  margin-top: 2px;
  display: block;
}

.source-progress {
  margin-top: 0.35rem;
  display: flex;
  align-items: center;
  gap: 0.35rem;
}

.source-progress-bar {
  flex: 1;
  height: 4px;
  background: rgba(255,255,255,0.08);
  border-radius: 2px;
  overflow: hidden;
}

.source-progress-fill {
  height: 100%;
  border-radius: 2px;
  transition: width 0.35s ease;
}

.source-progress-text {
  font-size: 0.7rem;
  color: var(--text-muted);
  white-space: nowrap;
  font-weight: 600;
}

.source-card.venn-hover-on { opacity: 1; }
.source-card.venn-hover-off { opacity: 0.45; }

.venn-controls {
  display: flex;
  flex-direction: column;
  gap: 0.65rem;
}

.control-group {
  background: var(--bg-inset);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-sm);
  padding: 0.55rem 0.65rem;
}

.control-group-label {
  display: block;
  font-size: var(--fs-xs);
  font-weight: 600;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 0.2rem;
}

.control-group-hint {
  display: block;
  font-size: 0.68rem;
  color: var(--text-muted);
  opacity: 0.8;
  margin-bottom: 0.45rem;
}

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

.overlap-row {
  margin-top: 0.4rem;
}

.control-divider {
  width: 1px;
  height: 22px;
  background: var(--border-card);
  margin: 0 0.15rem;
}

.presets-inline, .overlap-filters-grid {
  display: flex;
  gap: 0.35rem;
  flex-wrap: wrap;
}

.preset-pill, .overlap-pill {
  font-family: var(--font-title);
  font-size: var(--fs-sm);
  font-weight: 600;
  background: rgba(15, 23, 42, 0.55);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-sm);
  padding: 0.4rem 0.75rem;
  color: var(--text-secondary);
  cursor: pointer;
  transition: all var(--transition);
  white-space: nowrap;
}

.preset-pill:hover, .overlap-pill:hover {
  color: var(--text-primary);
  border-color: var(--border-strong);
  background: rgba(255,255,255,0.05);
}

.preset-pill.active, .overlap-pill.active {
  background: var(--accent-muted);
  border-color: var(--accent-border);
  color: var(--accent-strong);
}

.overlap-pill.selected {
  background: rgba(56, 189, 248, 0.12);
  border-color: rgba(56, 189, 248, 0.45);
  color: var(--text-primary);
}

.overlap-pill.selected.active {
  background: var(--accent-muted);
  border-color: var(--accent-strong);
  color: var(--accent-strong);
  box-shadow: 0 0 0 1px var(--accent-border);
}

.sources-group {
  margin-bottom: 0.55rem;
}

.sources-group .sources-grid {
  margin-top: 0;
}

.control-group-hint em {
  font-style: normal;
  color: var(--accent-strong);
  font-weight: 600;
}

.filter-state-legend {
  display: flex;
  flex-wrap: wrap;
  gap: 0.65rem;
  font-size: 0.68rem;
  color: var(--text-muted);
  margin-top: 0.15rem;
}

.legend-item {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
}

.legend-swatch {
  width: 10px;
  height: 10px;
  border-radius: 3px;
  flex-shrink: 0;
}

.legend-swatch-pending {
  background: rgba(56, 189, 248, 0.25);
  border: 1px solid rgba(56, 189, 248, 0.55);
}

.legend-swatch-applied {
  background: var(--accent-muted);
  border: 1px solid var(--accent-border);
}

.pending-status {
  font-size: var(--fs-xs);
  color: var(--accent-strong);
  background: rgba(56, 189, 248, 0.08);
  border: 1px solid rgba(56, 189, 248, 0.25);
  border-radius: var(--radius-sm);
  padding: 0.4rem 0.55rem;
  line-height: 1.4;
}

.pending-status[hidden] { display: none !important; }

.venn-region.preview-region .region-text {
  opacity: 1 !important;
}

.filter-apply-row {
  display: flex;
  align-items: center;
  gap: 0.45rem;
  flex-wrap: wrap;
  margin-top: 0.55rem;
  padding-top: 0.55rem;
  border-top: 1px solid var(--border-subtle);
}

#btn-apply-filters:disabled {
  opacity: 0.45;
  cursor: not-allowed;
}

.overlap-pill {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
}

.overlap-pill-count {
  font-weight: 700;
  color: var(--accent);
}

.overlap-pill.active .overlap-pill-count { color: var(--accent-strong); }

.compare-select {
  background: rgba(15, 23, 42, 0.55);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-sm);
  color: var(--text-primary);
  padding: 0.4rem 0.6rem;
  font-size: var(--fs-sm);
  font-family: var(--font-body);
  min-width: 140px;
  cursor: pointer;
  transition: border-color var(--transition);
}

.compare-select:hover,
.compare-select:focus {
  border-color: var(--border-strong);
  outline: none;
}

.compare-type-tabs {
  display: flex;
  gap: 2px;
  background: rgba(15, 23, 42, 0.55);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-sm);
  padding: 3px;
}

.compare-type-btn {
  background: transparent;
  border: none;
  color: var(--text-muted);
  padding: 0.35rem 0.65rem;
  border-radius: 6px;
  cursor: pointer;
  font-size: var(--fs-xs);
  font-weight: 600;
  font-family: var(--font-title);
  transition: all var(--transition);
}

.compare-type-btn:hover { color: var(--text-primary); }
.compare-type-btn.active {
  background: rgba(255,255,255,0.1);
  color: var(--text-primary);
}

.compare-collapsible {
  padding: 0;
  overflow: hidden;
}

.compare-collapsible[open] {
  padding-bottom: 0.55rem;
}

.compare-summary {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.55rem 0.65rem;
  font-size: var(--fs-xs);
  font-weight: 600;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  cursor: pointer;
  list-style: none;
  user-select: none;
  transition: color var(--transition);
}

.compare-summary::-webkit-details-marker { display: none; }

.compare-summary::after {
  content: "›";
  font-size: 1rem;
  color: var(--text-muted);
  transition: transform var(--transition);
}

.compare-collapsible[open] .compare-summary::after {
  transform: rotate(90deg);
}

.compare-summary:hover { color: var(--text-secondary); }

.compare-panel {
  padding: 0 0.65rem 0.1rem;
}

.venn-ellipse.ellipse-preview {
  fill-opacity: 0.75 !important;
  stroke-width: 3.5 !important;
  filter: url(#glow);
}

.venn-ellipse.ellipse-dimmed {
  fill-opacity: 0.1 !important;
  stroke-width: 1.5 !important;
  filter: none;
}

.venn-region {
  cursor: pointer;
  outline: none;
}

.venn-region .region-hit {
  fill: transparent;
  cursor: pointer;
}

.venn-region .region-text {
  font-family: var(--font-title);
  font-weight: 700;
  fill: #f8fafc;
  filter: url(#text-legibility);
  pointer-events: none;
  user-select: none;
  transition: opacity 0.15s ease, fill 0.15s ease;
}

.venn-region:focus-visible .region-hit {
  stroke: var(--accent);
  stroke-width: 2;
  stroke-dasharray: 4 3;
  fill: var(--accent-muted);
}

.venn-region:hover .region-text,
.venn-region:focus-visible .region-text {
  fill: #fff !important;
}

.venn-region.hub-region .region-text {
  font-weight: 800;
}

.venn-region.active-region .region-text {
  fill: #fff !important;
  font-weight: 800;
}

.venn-region.active-region .region-hit {
  fill: var(--accent-muted);
  stroke: var(--accent-strong);
  stroke-width: 2;
}

.venn-region.story-region:not(.active-region) .region-text {
  fill: #e2e8f0;
}

.venn-region.disabled { display: none; }

.venn-legend-item {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  font-size: var(--fs-xs);
  font-weight: 600;
  color: var(--text-secondary);
}

.venn-legend-item.blind75 .venn-legend-name { color: var(--color-blind75); }
.venn-legend-item.grind75 .venn-legend-name { color: var(--color-grind75); }
.venn-legend-item.leetcode150 .venn-legend-name { color: var(--color-leetcode150); }
.venn-legend-item.neetcode150 .venn-legend-name { color: var(--color-neetcode150); }

.venn-legend-dot {
  width: 9px;
  height: 9px;
  border-radius: 50%;
  flex-shrink: 0;
}

#venn-tooltip {
  position: absolute;
  background: rgba(15, 23, 42, 0.96);
  color: var(--text-primary);
  padding: 0.55rem 0.75rem;
  border-radius: var(--radius-sm);
  font-size: var(--fs-xs);
  line-height: 1.45;
  pointer-events: none;
  opacity: 0;
  transition: opacity var(--transition);
  z-index: 20;
  max-width: 260px;
  border: 1px solid var(--border-card);
  box-shadow: var(--shadow-md);
}

#venn-tooltip.visible { opacity: 1; }
#venn-tooltip .tooltip-title { font-weight: 700; margin-bottom: 4px; color: var(--text-primary); font-size: var(--fs-sm); }
#venn-tooltip .tooltip-pills { display: flex; flex-wrap: wrap; gap: 4px; margin-bottom: 4px; }
#venn-tooltip .tooltip-pill {
  font-size: 0.65rem;
  font-weight: 700;
  padding: 2px 6px;
  border-radius: 4px;
}
#venn-tooltip .tooltip-pill.blind75 { background: rgba(167,139,250,0.25); color: var(--color-blind75); }
#venn-tooltip .tooltip-pill.grind75 { background: rgba(56,189,248,0.25); color: var(--color-grind75); }
#venn-tooltip .tooltip-pill.leetcode150 { background: rgba(74,222,128,0.25); color: var(--color-leetcode150); }
#venn-tooltip .tooltip-pill.neetcode150 { background: rgba(251,191,36,0.25); color: var(--color-neetcode150); }
#venn-tooltip .tooltip-excludes { color: var(--text-muted); font-size: 0.7rem; margin-bottom: 4px; }
#venn-tooltip .tooltip-action { color: var(--accent-strong); font-size: 0.7rem; font-weight: 600; margin-top: 2px; }
#venn-tooltip .tooltip-detail { color: var(--text-muted); font-size: var(--fs-xs); }

/* ── Explorer panel ── */
.explorer-card {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  padding: 0 !important;
}

.explorer-header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 1rem;
  padding: 1rem 1.1rem 0;
  flex-shrink: 0;
}

.selection-info {
  display: flex;
  align-items: flex-start;
  gap: 0.65rem;
  min-width: 0;
}

.active-badge {
  font-size: var(--fs-xs);
  font-weight: 700;
  padding: 0.25rem 0.55rem;
  border-radius: 6px;
  background: var(--accent-muted);
  color: var(--accent-strong);
  border: 1px solid var(--accent-border);
  flex-shrink: 0;
  margin-top: 2px;
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.selection-text { min-width: 0; }

#current-selection-title {
  font-family: var(--font-title);
  font-size: var(--fs-lg);
  font-weight: 600;
  letter-spacing: -0.01em;
  color: var(--text-primary);
  line-height: 1.3;
}

.selection-desc {
  font-size: var(--fs-sm);
  color: var(--text-muted);
  margin-top: 0.2rem;
  line-height: 1.5;
  max-width: 52ch;
}

.header-actions {
  display: flex;
  gap: 0.4rem;
  flex-shrink: 0;
}

/* Active filter chips */
.active-filters-row {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 0.5rem;
  padding: 0 1.1rem;
  flex-shrink: 0;
}

.active-filters-label {
  font-size: var(--fs-xs);
  font-weight: 600;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.active-filters-chips {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
}

.filter-chip {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  background: var(--accent-muted);
  border: 1px solid var(--accent-border);
  font-size: var(--fs-xs);
  font-weight: 600;
  padding: 0.25rem 0.6rem;
  border-radius: 9999px;
  color: var(--accent-strong);
}

.filter-chip button {
  background: none;
  border: none;
  color: var(--text-muted);
  cursor: pointer;
  font-size: 1rem;
  line-height: 1;
  padding: 0;
  transition: color var(--transition);
}

.filter-chip button:hover { color: var(--text-primary); }

/* Toolbar */
.toolbar-row {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  flex-wrap: wrap;
  padding: 0.75rem 1rem;
  margin: 0 0.75rem;
  background: var(--bg-inset);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius);
}

.toolbar-group {
  display: flex;
  align-items: center;
  gap: 0.55rem;
}

.toolbar-filters {
  flex: 1 1 280px;
  min-width: 0;
}

.search-box {
  position: relative;
  flex: 1;
  min-width: 180px;
}

.search-icon {
  position: absolute;
  left: 12px;
  top: 50%;
  transform: translateY(-50%);
  width: 16px;
  height: 16px;
  color: var(--text-muted);
  pointer-events: none;
}

#search-input {
  width: 100%;
  background: rgba(15, 23, 42, 0.55);
  border: 1px solid var(--border-subtle);
  padding: 0.55rem 0.75rem 0.55rem 2.35rem;
  border-radius: var(--radius-sm);
  color: var(--text-primary);
  font-size: var(--fs-sm);
  font-family: var(--font-body);
  transition: border-color var(--transition), box-shadow var(--transition);
}

#search-input::placeholder { color: var(--text-muted); }

#search-input:focus {
  outline: none;
  border-color: var(--accent-border);
  box-shadow: 0 0 0 3px rgba(129, 140, 248, 0.15);
}

.difficulty-tabs {
  display: flex;
  gap: 2px;
  background: rgba(15, 23, 42, 0.55);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-sm);
  padding: 3px;
  flex-shrink: 0;
}

.tab-btn {
  background: transparent;
  border: none;
  color: var(--text-muted);
  padding: 0.4rem 0.7rem;
  border-radius: 6px;
  cursor: pointer;
  font-weight: 600;
  font-size: var(--fs-sm);
  font-family: var(--font-title);
  transition: all var(--transition);
  white-space: nowrap;
}

.tab-btn:hover { color: var(--text-primary); }

.tab-btn.active {
  background: rgba(255,255,255,0.1);
  color: var(--text-primary);
}

.subset-stats-inline {
  display: flex;
  gap: 0.75rem;
  font-size: var(--fs-xs);
  color: var(--text-muted);
  flex-wrap: wrap;
  padding: 0.35rem 0.65rem;
  background: rgba(15, 23, 42, 0.35);
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-subtle);
}

.subset-stats-inline .stat-item { white-space: nowrap; }

.subset-stats-inline b {
  font-family: var(--font-title);
  font-size: var(--fs-sm);
  color: var(--text-primary);
}

.export-row {
  display: flex;
  gap: 0.25rem;
  align-items: center;
  margin-left: auto;
}

.export-toast {
  font-size: var(--fs-xs);
  color: var(--solved);
  opacity: 0;
  transition: opacity 0.3s;
  font-weight: 600;
}

.export-toast.visible { opacity: 1; }

/* Buttons */
.btn {
  font-family: var(--font-title);
  font-weight: 600;
  font-size: var(--fs-sm);
  padding: 0.45rem 0.8rem;
  border-radius: var(--radius-sm);
  border: 1px solid transparent;
  cursor: pointer;
  transition: background var(--transition), border-color var(--transition), color var(--transition), box-shadow var(--transition);
  white-space: nowrap;
}

.btn-sm { font-size: var(--fs-xs); padding: 0.38rem 0.65rem; }

.btn-primary {
  background: var(--accent);
  border-color: var(--accent);
  color: #0f172a;
}

.btn-primary:hover {
  background: var(--accent-strong);
  border-color: var(--accent-strong);
}

.btn-secondary {
  background: rgba(255,255,255,0.07);
  border-color: var(--border-card);
  color: var(--text-primary);
}

.btn-secondary:hover { background: rgba(255,255,255,0.11); }

.btn-ghost {
  background: transparent;
  border-color: var(--border-subtle);
  color: var(--text-secondary);
}

.btn-ghost:hover {
  color: var(--text-primary);
  background: rgba(255,255,255,0.05);
  border-color: var(--border-card);
}

.btn:disabled {
  opacity: 0.4;
  cursor: not-allowed;
  pointer-events: none;
}

/* Categories & tags */
.categories-section,
.tags-section {
  flex-shrink: 0;
  padding: 0 1.1rem;
}

.tags-section {
  padding-top: 0.65rem;
  padding-bottom: 0.15rem;
}

.categories-header {
  display: flex;
  align-items: baseline;
  gap: 0.55rem;
  margin-bottom: 0.45rem;
}

.section-label {
  font-family: var(--font-title);
  font-size: var(--fs-xs);
  font-weight: 600;
  color: var(--text-secondary);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.section-hint {
  font-size: var(--fs-xs);
  color: var(--text-muted);
}

.categories-container {
  display: flex;
  flex-direction: row;
  flex-wrap: nowrap;
  gap: 0.55rem;
  overflow-x: auto;
  overflow-y: hidden;
  padding-bottom: 8px;
  scrollbar-width: thin;
  scrollbar-color: rgba(255,255,255,0.15) transparent;
}

.category-block {
  flex: 0 0 auto;
  min-width: 148px;
  max-width: 180px;
  background: var(--bg-inset);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-sm);
  padding: 0.55rem 0.7rem;
  cursor: pointer;
  transition: border-color var(--transition), background var(--transition), box-shadow var(--transition);
}

.category-block:hover {
  border-color: var(--accent-border);
  background: rgba(255,255,255,0.04);
}

.category-block.active {
  background: var(--accent-muted);
  border-color: var(--accent-border);
  box-shadow: 0 0 0 1px var(--accent-border);
}

.category-block-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 0.4rem;
  margin-bottom: 6px;
}

.category-block-title {
  font-size: var(--fs-sm);
  font-weight: 600;
  color: var(--text-primary);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.category-block-count {
  font-family: var(--font-title);
  font-size: var(--fs-sm);
  font-weight: 700;
  color: var(--accent);
  flex-shrink: 0;
}

.category-bar-bg {
  width: 100%;
  height: 5px;
  background: rgba(255,255,255,0.06);
  border-radius: 3px;
  overflow: hidden;
}

.category-bar-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--accent), var(--color-grind75));
  border-radius: 3px;
  transition: width 0.4s ease;
}

.categories-container::-webkit-scrollbar { height: 6px; }
.categories-container::-webkit-scrollbar-thumb {
  background: rgba(255,255,255,0.14);
  border-radius: 3px;
}

.category-empty {
  font-size: var(--fs-sm);
  color: var(--text-muted);
  padding: 0.35rem 0;
}

.tags-panel {
  background: var(--bg-inset);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-sm);
  padding: 0.65rem 0.75rem;
}

.tags-container {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.45rem;
  max-height: 96px;
  overflow-y: auto;
  padding-right: 2px;
  scrollbar-width: thin;
  scrollbar-color: rgba(255,255,255,0.15) transparent;
}

.tags-container::-webkit-scrollbar { width: 6px; height: 6px; }
.tags-container::-webkit-scrollbar-thumb {
  background: rgba(255,255,255,0.14);
  border-radius: 3px;
}

.tag-block {
  flex: 0 0 auto;
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  background: rgba(56, 189, 248, 0.1);
  border: 1px solid rgba(56, 189, 248, 0.24);
  border-radius: 999px;
  padding: 0.3rem 0.7rem;
  cursor: pointer;
  user-select: none;
  transition: border-color var(--transition), background var(--transition), box-shadow var(--transition), transform var(--transition);
}

.tag-block:hover {
  border-color: rgba(56, 189, 248, 0.45);
  background: rgba(56, 189, 248, 0.16);
  transform: translateY(-1px);
}

.tag-block.active {
  background: rgba(56, 189, 248, 0.24);
  border-color: rgba(56, 189, 248, 0.62);
  box-shadow: 0 0 0 1px rgba(56, 189, 248, 0.35);
}

.tag-block-name {
  font-size: var(--fs-xs);
  font-weight: 600;
  color: #7dd3fc;
  white-space: nowrap;
  line-height: 1.2;
}

.tag-block-count {
  font-family: var(--font-title);
  font-size: 0.68rem;
  font-weight: 700;
  color: var(--text-secondary);
  background: rgba(255,255,255,0.08);
  border-radius: 999px;
  padding: 0.1rem 0.38rem;
  line-height: 1.2;
}

.tags-empty {
  font-size: var(--fs-sm);
  color: var(--text-muted);
  font-style: italic;
}

/* Table */
.table-container {
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius);
  background: var(--bg-inset);
  margin: 0 0.75rem;
  overflow-x: auto;
}

.questions-table {
  width: 100%;
  min-width: 980px;
  border-collapse: collapse;
  font-size: var(--fs-sm);
  table-layout: fixed;
}

.questions-table col.col-done { width: 56px; }
.questions-table col.col-id { width: 56px; }
.questions-table col.col-question { width: 22%; }
.questions-table col.col-difficulty { width: 92px; }
.questions-table col.col-category { width: 128px; }
.questions-table col.col-original { width: 128px; }
.questions-table col.col-tags { width: 150px; }
.questions-table col.col-sources { width: 100px; }
.questions-table col.col-solutions { width: 72px; }
.questions-table col.col-link { width: 56px; }

.questions-table th {
  background: rgba(15, 23, 42, 0.98);
  padding: 0.75rem 0.85rem;
  font-family: var(--font-title);
  font-weight: 600;
  font-size: var(--fs-xs);
  color: var(--text-muted);
  border-bottom: 1px solid var(--border-card);
  cursor: pointer;
  user-select: none;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  transition: color var(--transition);
  white-space: nowrap;
}

.questions-table th:hover { color: var(--text-secondary); }

.questions-table th:nth-child(1),
.questions-table td:nth-child(1) { text-align: center; }

.questions-table th:nth-child(9),
.questions-table td:nth-child(9),
.questions-table th:nth-child(10),
.questions-table td:nth-child(10) { text-align: center; }

.questions-table th.sort-asc::after,
.questions-table th.sort-desc::after {
  margin-left: 4px;
  font-size: 0.65rem;
  color: var(--accent);
}

.questions-table th.sort-asc::after { content: "▲"; }
.questions-table th.sort-desc::after { content: "▼"; }

.questions-table td {
  padding: 0.7rem 0.85rem;
  border-bottom: 1px solid var(--border-subtle);
  vertical-align: middle;
  line-height: 1.45;
}

.questions-table td:first-child,
.questions-table th:first-child { text-align: center; }

.questions-table tbody tr:nth-child(even) {
  background: rgba(255,255,255,0.02);
}

.questions-table tbody tr:hover {
  background: rgba(129, 140, 248, 0.08);
}

.questions-table tbody tr.row-solved { opacity: 0.7; }
.questions-table tbody tr.row-solved .question-name-link {
  text-decoration: line-through;
  color: var(--text-muted);
}

.questions-table tbody tr:last-child td {
  border-bottom: none;
}

.solved-checkbox {
  width: 16px;
  height: 16px;
  accent-color: var(--solved);
  cursor: pointer;
}

.question-name-link {
  color: var(--text-primary);
  text-decoration: none;
  font-weight: 500;
  font-size: var(--fs-sm);
  display: block;
  transition: color var(--transition);
  word-break: break-word;
}

.question-name-link:hover { color: var(--accent-strong); }

.badge-difficulty {
  display: inline-block;
  padding: 0.2rem 0.5rem;
  border-radius: 6px;
  font-size: var(--fs-xs);
  font-weight: 700;
  text-align: center;
  letter-spacing: 0.02em;
}

.badge-difficulty.easy { background: var(--easy-bg); color: var(--easy); }
.badge-difficulty.medium { background: var(--medium-bg); color: var(--medium); }
.badge-difficulty.hard { background: var(--hard-bg); color: var(--hard); }

.source-pills { display: flex; flex-wrap: wrap; gap: 3px; }

.source-pill {
  font-size: 0.7rem;
  font-weight: 700;
  padding: 3px 6px;
  border-radius: 5px;
  letter-spacing: 0.03em;
}

.source-pill.blind75 { background: rgba(167,139,250,0.2); color: var(--color-blind75); }
.source-pill.grind75 { background: rgba(56,189,248,0.2); color: var(--color-grind75); }
.source-pill.leetcode150 { background: rgba(74,222,128,0.2); color: var(--color-leetcode150); }
.source-pill.neetcode150 { background: rgba(251,191,36,0.2); color: var(--color-neetcode150); }

.link-icon-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
  border-radius: var(--radius-sm);
  background: rgba(255,255,255,0.04);
  border: 1px solid var(--border-subtle);
  color: var(--text-muted);
  text-decoration: none;
  transition: all var(--transition);
}

.link-icon-btn:hover {
  background: var(--accent-muted);
  border-color: var(--accent-border);
  color: var(--accent-strong);
}

.link-icon-btn svg { width: 14px; height: 14px; }

.solution-link-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 36px;
  padding: 0.2rem 0.5rem;
  border-radius: 999px;
  border: 1px solid rgba(251, 191, 36, 0.35);
  background: rgba(251, 191, 36, 0.12);
  color: #fbbf24;
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.04em;
  text-decoration: none;
  transition: background var(--transition), border-color var(--transition), color var(--transition);
}

.solution-link-btn:hover {
  background: rgba(251, 191, 36, 0.22);
  border-color: rgba(251, 191, 36, 0.55);
  color: #fde68a;
}

.solution-empty {
  color: var(--text-muted);
  font-size: var(--fs-sm);
}

.category-tag {
  font-size: var(--fs-xs);
  color: var(--text-secondary);
  background: rgba(255,255,255,0.04);
  border: 1px solid var(--border-subtle);
  border-radius: 6px;
  padding: 0.25rem 0.5rem;
  display: inline-block;
  max-width: 100%;
  word-break: break-word;
}

.original-category-tag {
  font-size: var(--fs-xs);
  color: var(--text-muted);
  background: rgba(255,255,255,0.02);
  border: 1px dashed rgba(255,255,255,0.08);
  border-radius: 6px;
  padding: 0.25rem 0.5rem;
  display: inline-block;
  max-width: 100%;
  word-break: break-word;
}

.tag-pills {
  display: flex;
  flex-wrap: wrap;
  gap: 0.25rem;
}

.tag-pill {
  font-size: 0.68rem;
  font-weight: 600;
  color: #7dd3fc;
  background: rgba(56, 189, 248, 0.1);
  border: 1px solid rgba(56, 189, 248, 0.22);
  border-radius: 999px;
  padding: 0.12rem 0.45rem;
  white-space: nowrap;
}

.tag-empty {
  color: var(--text-muted);
  font-size: var(--fs-xs);
}

.table-container::-webkit-scrollbar { height: 8px; width: 8px; }
.table-container::-webkit-scrollbar-thumb {
  background: rgba(255,255,255,0.14);
  border-radius: 4px;
}

/* Pagination & empty state */
.pagination-row {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.75rem;
  padding: 0.5rem 1.1rem 1rem;
  flex-shrink: 0;
}

.page-info {
  font-size: var(--fs-sm);
  color: var(--text-muted);
  font-family: var(--font-title);
  font-weight: 600;
  min-width: 100px;
  text-align: center;
}

.no-results {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 4rem 1.5rem;
  text-align: center;
  gap: 0.35rem;
}

.no-results-icon {
  font-size: 2rem;
  color: var(--text-muted);
  opacity: 0.5;
  margin-bottom: 0.25rem;
}

.no-results-title {
  font-family: var(--font-title);
  font-size: var(--fs-md);
  font-weight: 600;
  color: var(--text-secondary);
}

.no-results-hint {
  font-size: var(--fs-sm);
  color: var(--text-muted);
}

.easy-text b { color: var(--easy); }
.medium-text b { color: var(--medium); }
.hard-text b { color: var(--hard); }
.solved-text b { color: var(--solved); }

/* Global scrollbar */
::-webkit-scrollbar { width: 10px; height: 10px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb {
  background: rgba(255,255,255,0.12);
  border-radius: 5px;
  border: 2px solid transparent;
  background-clip: padding-box;
}
::-webkit-scrollbar-thumb:hover { background: rgba(255,255,255,0.2); background-clip: padding-box; }

/* Focus & accessibility */
:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

button:focus:not(:focus-visible),
input:focus:not(:focus-visible) {
  outline: none;
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
}

/* Responsive */
@media (max-width: 1280px) {
  .venn-explorer-body { grid-template-columns: minmax(0, 1fr) minmax(260px, 0.95fr); }
  .toolbar-stats { width: 100%; order: 3; }
  .export-row { margin-left: 0; width: 100%; justify-content: flex-end; }
}

@media (max-width: 900px) {
  .venn-explorer-body {
    grid-template-columns: 1fr;
  }

  .venn-stage {
    border-right: none;
    border-bottom: 1px solid var(--border-subtle);
  }

  .venn-wrapper {
    max-height: 360px;
    margin: 0.35rem auto;
    padding: 0.5rem;
  }

  .venn-controls-panel { overflow: visible; }
}

@media (max-width: 768px) {
  body { padding: 1rem; }
  .app-header { flex-direction: column; align-items: stretch; }
  .header-nav { justify-content: flex-start; }
  .header-stats { display: grid; grid-template-columns: repeat(4, 1fr); gap: 0.4rem; }
  .header-stats .stat-pill { min-width: 0; }
  .explorer-header { flex-direction: column; }
  .header-actions { width: 100%; }
  .header-actions .btn { flex: 1; }
  .toolbar-row { flex-direction: column; align-items: stretch; margin: 0 0.5rem; }
  .toolbar-filters { flex-direction: column; width: 100%; }
  .difficulty-tabs { width: 100%; }
  .difficulty-tabs .tab-btn { flex: 1; text-align: center; }
  .subset-stats-inline { width: 100%; justify-content: space-between; }
  .table-container { margin: 0 0.5rem; }
  .questions-table { min-width: 860px; }
  .questions-table .col-original,
  .questions-table th[data-sort="original_category"],
  .questions-table td:nth-child(6) { display: none; }
}

@media (max-width: 480px) {
  .sources-grid { grid-template-columns: 1fr; }
  .header-stats { grid-template-columns: repeat(2, 1fr); }
  .control-row { flex-direction: column; align-items: stretch; }
  .control-divider { display: none; }
  .compare-select { width: 100%; max-width: none; }
}