/* ============================================================
   Algorithm Arsenal — main.css
   Premium dark theme with glassmorphism, neon accents,
   smooth animations, and full responsive layout.
   ============================================================ */

/* ── Design tokens ──────────────────────────────────────────── */
:root {
  --bg-0:          #080c14;
  --bg-1:          #0d1220;
  --bg-2:          #111827;
  --bg-3:          #1a2235;
  --surface:       rgba(255, 255, 255, 0.03);
  --border-subtle: rgba(255, 255, 255, 0.06);
  --border:        rgba(255, 255, 255, 0.10);
  --border-strong: rgba(255, 255, 255, 0.18);

  --text-1:   #e2e8f0;
  --text-2:   #94a3b8;
  --text-3:   #475569;

  --cyan:     #00d4ff;
  --cyan-dim: rgba(0, 212, 255, 0.15);
  --purple:   #a855f7;
  --purple-dim: rgba(168, 85, 247, 0.15);
  --green:    #22c55e;
  --amber:    #f59e0b;
  --red:      #ef4444;

  --easy-bg:   rgba(34, 197, 94, 0.12);
  --medium-bg: rgba(245, 158, 11, 0.12);
  --hard-bg:   rgba(239, 68, 68, 0.12);

  --font-sans: "Inter", system-ui, sans-serif;
  --font-mono: "JetBrains Mono", "Fira Code", monospace;

  --radius-sm: 6px;
  --radius:    10px;
  --radius-lg: 16px;
  --radius-xl: 24px;

  --shadow-card: 0 4px 24px rgba(0, 0, 0, 0.4);
  --shadow-glow-cyan:   0 0 30px rgba(0, 212, 255, 0.15);
  --shadow-glow-easy:   0 0 30px rgba(34, 197, 94, 0.12);
  --shadow-glow-medium: 0 0 30px rgba(245, 158, 11, 0.12);
  --shadow-glow-hard:   0 0 30px rgba(239, 68, 68, 0.12);

  --nav-h: 64px;
  --panel-w: min(680px, 95vw);
}

[data-theme="light"] {
  --bg-0: #f1f5f9;
  --bg-1: #ffffff;
  --bg-2: #f8fafc;
  --bg-3: #e2e8f0;
  --surface: rgba(0, 0, 0, 0.03);
  --border-subtle: rgba(0, 0, 0, 0.06);
  --border: rgba(0, 0, 0, 0.10);
  --border-strong: rgba(0, 0, 0, 0.18);
  --text-1: #0f172a;
  --text-2: #475569;
  --text-3: #94a3b8;
}

/* ── Reset & base ───────────────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html {
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
}

body {
  font-family: var(--font-sans);
  font-size: 15px;
  line-height: 1.6;
  color: var(--text-1);
  background: var(--bg-0);
  overflow-x: hidden;
  min-height: 100vh;
}

a { color: inherit; text-decoration: none; }
button { font-family: var(--font-sans); cursor: pointer; border: none; background: none; }
select { font-family: var(--font-sans); }
img, svg { display: block; }

/* ── Ambient background ─────────────────────────────────────── */
.bg-dots {
  position: fixed;
  inset: 0;
  background-image:
    radial-gradient(circle, rgba(255,255,255,0.025) 1px, transparent 1px);
  background-size: 36px 36px;
  pointer-events: none;
  z-index: 0;
}
[data-theme="light"] .bg-dots {
  background-image:
    radial-gradient(circle, rgba(0,0,0,0.04) 1px, transparent 1px);
}

.bg-orb {
  position: fixed;
  border-radius: 50%;
  filter: blur(100px);
  pointer-events: none;
  z-index: 0;
  opacity: 0;
  animation: orbFade 2s ease forwards;
}
.bg-orb--1 {
  width: 700px; height: 700px;
  background: radial-gradient(circle, rgba(0,212,255,0.18), transparent 70%);
  top: -200px; left: -200px;
  animation-delay: 0.2s;
  animation: orbFade 2s ease 0.2s forwards, orb1Float 22s ease-in-out 2.2s infinite alternate;
}
.bg-orb--2 {
  width: 600px; height: 600px;
  background: radial-gradient(circle, rgba(168,85,247,0.16), transparent 70%);
  bottom: -150px; right: -100px;
  animation: orbFade 2s ease 0.5s forwards, orb2Float 28s ease-in-out 2.5s infinite alternate;
}
.bg-orb--3 {
  width: 400px; height: 400px;
  background: radial-gradient(circle, rgba(34,197,94,0.1), transparent 70%);
  top: 50%; left: 50%;
  transform: translate(-50%, -50%);
  animation: orbFade 2s ease 0.8s forwards, orb3Float 18s ease-in-out 2.8s infinite alternate;
}

@keyframes orbFade { to { opacity: 1; } }
@keyframes orb1Float { from { transform: translate(0,0); } to { transform: translate(80px, 60px); } }
@keyframes orb2Float { from { transform: translate(0,0); } to { transform: translate(-60px, -80px); } }
@keyframes orb3Float { from { transform: translate(-50%, -50%); } to { transform: translate(calc(-50% + 40px), calc(-50% + 30px)); } }

/* ── Layout shell ───────────────────────────────────────────── */
#main-content { position: relative; z-index: 1; }

/* ── Navbar ─────────────────────────────────────────────────── */
.navbar {
  position: fixed;
  top: 0; left: 0; right: 0;
  height: var(--nav-h);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 clamp(16px, 4vw, 48px);
  background: rgba(8, 12, 20, 0.7);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--border-subtle);
  z-index: 100;
}
[data-theme="light"] .navbar {
  background: rgba(248, 250, 252, 0.8);
}

.nav-brand {
  display: flex;
  align-items: center;
  gap: 10px;
  font-weight: 700;
  font-size: 17px;
  letter-spacing: -0.3px;
}
.nav-icon { font-size: 22px; }
.nav-title {
  background: linear-gradient(to right, #ff0036, #e3f94c, #0b55d1, #ff0036);
  background-size: 300% 100%;
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  animation: gradient-pan 8s ease-in-out infinite alternate;
}

.nav-controls { display: flex; align-items: center; gap: 12px; }

.theme-toggle {
  width: 38px; height: 38px;
  border-radius: 50%;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text-1);
  display: grid; place-items: center;
  font-size: 16px;
  transition: all 0.2s;
  backdrop-filter: blur(8px);
}
.theme-toggle:hover { border-color: var(--cyan); box-shadow: var(--shadow-glow-cyan); }

.nav-github {
  display: flex; align-items: center; gap: 7px;
  padding: 8px 16px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text-1);
  font-size: 13px;
  font-weight: 500;
  transition: all 0.2s;
}
.nav-github:hover {
  border-color: var(--cyan);
  color: var(--cyan);
  box-shadow: var(--shadow-glow-cyan);
}

/* ── Hero ───────────────────────────────────────────────────── */
.hero {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: calc(var(--nav-h) + 40px) clamp(16px, 6vw, 80px) 80px;
}

.hero-inner {
  max-width: 800px;
  animation: heroIn 0.8s cubic-bezier(0.22, 1, 0.36, 1) both;
}
@keyframes heroIn {
  from { opacity: 0; transform: translateY(30px); }
  to   { opacity: 1; transform: translateY(0); }
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 6px 16px;
  border-radius: 99px;
  border: 1px solid rgba(0, 212, 255, 0.25);
  background: rgba(0, 212, 255, 0.08);
  color: var(--cyan);
  font-size: 12px;
  font-weight: 600;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  margin-bottom: 28px;
}

.pulse-dot {
  width: 7px; height: 7px;
  border-radius: 50%;
  background: var(--cyan);
  box-shadow: 0 0 8px var(--cyan);
  animation: pulse 2s ease-in-out infinite;
}
@keyframes pulse {
  0%, 100% { opacity: 1; transform: scale(1); }
  50%       { opacity: 0.6; transform: scale(0.8); }
}

.hero-title {
  font-size: clamp(42px, 8vw, 90px);
  font-weight: 800;
  letter-spacing: -2px;
  line-height: 1.05;
  margin-bottom: 20px;
}

.gradient-text {
  background: linear-gradient(to right, #ff0036, #e3f94c, #0b55d1, #ff0036);
  background-size: 300% 100%;
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  animation: gradient-pan 8s ease-in-out infinite alternate;
}
@keyframes gradient-pan {
  0%   { background-position: 0% 50%; }
  100% { background-position: 100% 50%; }
}

.hero-subtitle {
  font-size: clamp(15px, 2vw, 18px);
  color: var(--text-2);
  max-width: 560px;
  margin: 0 auto 48px;
  line-height: 1.7;
}

.hero-counters {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0;
  flex-wrap: wrap;
  padding: 28px 36px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-xl);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  gap: 8px;
}

.hero-counter {
  display: flex;
  flex-direction: column;
  align-items: center;
  padding: 0 28px;
}
.hero-counter-divider {
  width: 1px; height: 44px;
  background: var(--border);
}

.counter-value {
  font-family: var(--font-mono);
  font-size: clamp(28px, 5vw, 42px);
  font-weight: 700;
  letter-spacing: -1px;
  color: var(--text-1);
}
.counter-label {
  font-size: 12px;
  font-weight: 500;
  color: var(--text-3);
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin-top: 2px;
}

.easy-counter   .counter-value { color: var(--green); }
.medium-counter .counter-value { color: var(--amber); }
.hard-counter   .counter-value { color: var(--red); }

/* ── Shared section styles ──────────────────────────────────── */
section { padding: 80px clamp(16px, 5vw, 64px); }

.section-header {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 8px;
  margin-bottom: 32px;
}
.section-title {
  font-size: clamp(22px, 3vw, 28px);
  font-weight: 700;
  letter-spacing: -0.5px;
}
.section-sub {
  font-size: 13px;
  color: var(--text-3);
}

/* ── Galaxy ─────────────────────────────────────────────────── */
.galaxy-section { padding-top: 0; }

.galaxy-legend {
  display: flex;
  gap: 20px;
  flex-wrap: wrap;
  margin-bottom: 20px;
}
.legend-item {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: 12px;
  color: var(--text-2);
  font-weight: 500;
}
.legend-dot {
  width: 10px; height: 10px;
  border-radius: 50%;
}
.legend-item.easy   .legend-dot { background: var(--green); }
.legend-item.medium .legend-dot { background: var(--amber); }
.legend-item.hard   .legend-dot { background: var(--red); }
.legend-item.unknown .legend-dot { background: var(--text-3); }

.galaxy-wrap {
  overflow-x: auto;
  padding-bottom: 8px;
}
.galaxy-grid {
  display: flex;
  flex-wrap: wrap;
  gap: 4px;
  padding: 20px;
  background: var(--surface);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  backdrop-filter: blur(8px);
  min-height: 60px;
}

.galaxy-dot {
  width: 9px; height: 9px;
  border-radius: 50%;
  cursor: pointer;
  transition: transform 0.15s, box-shadow 0.15s;
  flex-shrink: 0;
}
.galaxy-dot:hover { transform: scale(2.2); }
.galaxy-dot.easy   { background: var(--green); }
.galaxy-dot.medium { background: var(--amber); }
.galaxy-dot.hard   { background: var(--red); }
.galaxy-dot.unknown { background: var(--text-3); opacity: 0.5; }
.galaxy-dot.easy:hover   { box-shadow: 0 0 8px var(--green); }
.galaxy-dot.medium:hover { box-shadow: 0 0 8px var(--amber); }
.galaxy-dot.hard:hover   { box-shadow: 0 0 8px var(--red); }

.galaxy-tooltip {
  position: fixed;
  padding: 6px 12px;
  background: var(--bg-3);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  font-size: 12px;
  font-family: var(--font-mono);
  color: var(--text-1);
  pointer-events: none;
  z-index: 200;
  opacity: 0;
  transition: opacity 0.15s;
  white-space: nowrap;
  box-shadow: var(--shadow-card);
}
.galaxy-tooltip.visible { opacity: 1; }

/* ── Stats ──────────────────────────────────────────────────── */
.stats-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 20px;
}

.stats-card {
  position: relative;
  padding: 28px;
  background: linear-gradient(145deg, var(--surface) 0%, rgba(0,0,0,0) 100%);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  backdrop-filter: blur(16px);
  overflow: hidden;
  transition: transform 0.3s cubic-bezier(0.22, 1, 0.36, 1), border-color 0.3s, box-shadow 0.3s;
}
.stats-card::before {
  content: '';
  position: absolute;
  top: 0; left: -100%;
  width: 50%; height: 100%;
  background: linear-gradient(90deg, transparent, rgba(255,255,255,0.06), transparent);
  transform: skewX(-20deg);
  transition: left 0.6s ease-in-out;
  pointer-events: none;
}
.stats-card:hover {
  transform: translateY(-6px);
  border-color: rgba(0, 212, 255, 0.3);
  box-shadow: 0 10px 30px -10px rgba(0, 0, 0, 0.5), 0 0 20px rgba(0, 212, 255, 0.1);
}
.stats-card:hover::before {
  left: 150%;
}

.stats-card-title {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 14px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  color: var(--text-1);
  margin-bottom: 24px;
}

/* Difficulty bars */
.diff-bar-row {
  display: grid;
  grid-template-columns: 60px 1fr 40px;
  align-items: center;
  gap: 12px;
  margin-bottom: 14px;
}
.diff-bar-label { font-size: 13px; font-weight: 600; }
.diff-bar-track {
  height: 6px;
  background: var(--border-subtle);
  border-radius: 99px;
  overflow: hidden;
}
.diff-bar-fill {
  height: 100%;
  border-radius: 99px;
  width: 0;
  transition: width 1.2s cubic-bezier(0.22, 1, 0.36, 1);
}
.diff-bar-count { font-family: var(--font-mono); font-size: 13px; color: var(--text-2); text-align: right; }
.easy-fill   { background: linear-gradient(90deg, var(--green), #4ade80); }
.medium-fill { background: linear-gradient(90deg, var(--amber), #fcd34d); }
.hard-fill   { background: linear-gradient(90deg, var(--red), #f87171); }

/* Topic bars */
.topic-bar-row {
  display: grid;
  grid-template-columns: 1fr auto;
  align-items: center;
  gap: 10px;
  margin-bottom: 10px;
}
.topic-bar-inner { display: flex; align-items: center; gap: 8px; }
.topic-name { font-size: 13px; color: var(--text-2); flex: 1; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.topic-track {
  flex: 1;
  height: 4px;
  background: var(--border-subtle);
  border-radius: 99px;
  overflow: hidden;
  min-width: 60px;
}
.topic-fill {
  height: 100%;
  border-radius: 99px;
  background: linear-gradient(90deg, var(--cyan), var(--purple));
  width: 0;
  transition: width 1.2s cubic-bezier(0.22, 1, 0.36, 1);
}
.topic-count { font-family: var(--font-mono); font-size: 12px; color: var(--text-3); }

/* Language grid */
.lang-grid { display: flex; flex-wrap: wrap; gap: 10px; }
.lang-chip {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 14px;
  border-radius: var(--radius);
  border: 1px solid var(--border-subtle);
  background: var(--surface);
  font-size: 13px;
  font-weight: 500;
  transition: all 0.2s;
}
.lang-chip:hover { border-color: var(--cyan); color: var(--cyan); }
.lang-chip-count {
  font-family: var(--font-mono);
  font-size: 11px;
  color: var(--text-3);
  background: var(--bg-3);
  padding: 1px 6px;
  border-radius: 99px;
}

/* ── Filters bar ────────────────────────────────────────────── */
.filters-bar {
  position: sticky;
  top: var(--nav-h);
  z-index: 50;
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 12px;
  padding: 16px 0;
  margin-bottom: 28px;
  background: linear-gradient(to bottom, var(--bg-0) 85%, transparent);
}

.search-wrapper {
  position: relative;
  flex: 1;
  min-width: 200px;
  max-width: 400px;
}
.search-icon {
  position: absolute;
  left: 13px; top: 50%;
  transform: translateY(-50%);
  color: var(--text-3);
  pointer-events: none;
}
.search-input {
  width: 100%;
  padding: 10px 36px 10px 40px;
  background: var(--bg-1);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  color: var(--text-1);
  font-family: var(--font-mono);
  font-size: 13px;
  outline: none;
  transition: all 0.2s;
}
.search-input:focus {
  border-color: var(--cyan);
  box-shadow: 0 0 0 3px rgba(0, 212, 255, 0.08);
}
.search-input::placeholder { color: var(--text-3); }
.search-kbd {
  position: absolute;
  right: 11px; top: 50%;
  transform: translateY(-50%);
  padding: 2px 6px;
  background: var(--bg-3);
  border-radius: 4px;
  font-size: 11px;
  font-family: var(--font-mono);
  color: var(--text-3);
  border: 1px solid var(--border-subtle);
  pointer-events: none;
}
.search-input:focus ~ .search-kbd { opacity: 0; }

.filter-group {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
}

/* Custom select */
.filter-select {
  appearance: none;
  -webkit-appearance: none;
  padding: 10px 32px 10px 14px;
  background: var(--bg-1)
    url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='12' viewBox='0 0 24 24' fill='none' stroke='%2364748b' stroke-width='2.5'%3E%3Cpath d='m6 9 6 6 6-6'/%3E%3C/svg%3E")
    no-repeat right 10px center;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  color: var(--text-1);
  font-size: 13px;
  font-family: var(--font-sans);
  outline: none;
  cursor: pointer;
  transition: all 0.2s;
}
.filter-select:focus,
.filter-select:hover { border-color: var(--cyan); }

.clear-filters-btn {
  padding: 10px 16px;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text-2);
  font-size: 13px;
  font-weight: 500;
  transition: all 0.2s;
  white-space: nowrap;
}
.clear-filters-btn:hover { border-color: var(--red); color: var(--red); }

.results-count {
  font-family: var(--font-mono);
  font-size: 13px;
  color: var(--text-3);
}

/* ── Problem Grid ───────────────────────────────────────────── */
.problems-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 14px;
}

/* Problem Card */
.problem-card {
  position: relative;
  padding: 18px 20px;
  background: linear-gradient(145deg, var(--surface) 0%, rgba(0,0,0,0) 100%);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  cursor: pointer;
  overflow: hidden;
  backdrop-filter: blur(12px);
  transition: transform 0.3s cubic-bezier(0.22, 1, 0.36, 1), border-color 0.3s, box-shadow 0.3s;
}
.problem-card::before {
  content: '';
  position: absolute;
  top: 0; left: -100%;
  width: 50%; height: 100%;
  background: linear-gradient(90deg, transparent, rgba(255,255,255,0.06), transparent);
  transform: skewX(-20deg);
  transition: left 0.6s ease-in-out;
  pointer-events: none;
  z-index: 0;
}
.problem-card > * {
  position: relative;
  z-index: 1;
}
.problem-card:hover { transform: translateY(-5px); }
.problem-card:hover::before { left: 150%; }

.problem-card[data-diff="Easy"]:hover    { border-color: rgba(34,197,94,0.35); box-shadow: 0 8px 20px -8px rgba(0,0,0,0.5), var(--shadow-glow-easy); }
.problem-card[data-diff="Medium"]:hover  { border-color: rgba(245,158,11,0.35); box-shadow: 0 8px 20px -8px rgba(0,0,0,0.5), var(--shadow-glow-medium); }
.problem-card[data-diff="Hard"]:hover    { border-color: rgba(239,68,68,0.35); box-shadow: 0 8px 20px -8px rgba(0,0,0,0.5), var(--shadow-glow-hard); }

.card-doodle {
  position: absolute;
  bottom: 12px;
  right: 12px;
  width: 48px;
  height: 48px;
  opacity: 0.15;
  transition: opacity 0.3s, transform 0.3s, filter 0.3s;
  pointer-events: none;
  z-index: 0;
  filter: grayscale(100%) brightness(1.5);
}
[data-theme="light"] .card-doodle {
  filter: grayscale(100%) brightness(0.5);
}
.problem-card:hover .card-doodle {
  opacity: 0.85;
  transform: scale(1.15) rotate(8deg);
  filter: none;
}

.card-top {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 8px;
  margin-bottom: 10px;
}
.card-num {
  font-family: var(--font-mono);
  font-size: 11px;
  font-weight: 600;
  color: var(--text-3);
  letter-spacing: 0.05em;
}
.card-diff {
  font-size: 11px;
  font-weight: 700;
  padding: 2px 8px;
  border-radius: 99px;
}
.card-diff.easy   { background: var(--easy-bg);   color: var(--green); }
.card-diff.medium { background: var(--medium-bg);  color: var(--amber); }
.card-diff.hard   { background: var(--hard-bg);    color: var(--red); }
.card-diff.unknown { background: var(--bg-3); color: var(--text-3); }

.card-title {
  font-size: 14px;
  font-weight: 600;
  color: var(--text-1);
  line-height: 1.4;
  margin-bottom: 10px;
}

.card-topics {
  display: flex;
  flex-wrap: wrap;
  gap: 5px;
  margin-bottom: 12px;
}
.card-topic {
  font-size: 11px;
  padding: 2px 8px;
  border-radius: 99px;
  background: var(--bg-3);
  color: var(--text-2);
  border: 1px solid var(--border-subtle);
}

.card-bottom {
  display: flex;
  gap: 5px;
  flex-wrap: wrap;
}
.card-lang {
  font-family: var(--font-mono);
  font-size: 11px;
  padding: 2px 8px;
  border-radius: var(--radius-sm);
  background: var(--cyan-dim);
  color: var(--cyan);
  border: 1px solid rgba(0,212,255,0.2);
  font-weight: 600;
}

/* ── Loading / Empty states ─────────────────────────────────── */
.loading-state,
.empty-state {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 16px;
  padding: 80px 20px;
  color: var(--text-2);
  text-align: center;
}
.loading-state[hidden], .empty-state[hidden] { display: none; }

.spinner {
  width: 40px; height: 40px;
  border: 3px solid var(--border);
  border-top-color: var(--cyan);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }

.empty-icon { font-size: 48px; }

.btn-secondary {
  padding: 10px 24px;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text-1);
  font-size: 14px;
  font-weight: 500;
  transition: all 0.2s;
  cursor: pointer;
}
.btn-secondary:hover { border-color: var(--cyan); color: var(--cyan); }

/* ── Detail Overlay & Panel ─────────────────────────────────── */
.detail-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.65);
  backdrop-filter: blur(6px);
  z-index: 150;
  display: flex;
  justify-content: flex-end;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.3s;
}
.detail-overlay:not([hidden]) {
  opacity: 1;
  pointer-events: all;
}
.detail-overlay[hidden] { display: none; }

.detail-panel {
  width: var(--panel-w);
  height: 100%;
  background: var(--bg-1);
  border-left: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  transform: translateX(100%);
  transition: transform 0.35s cubic-bezier(0.22, 1, 0.36, 1);
  overflow: hidden;
}
.detail-overlay:not([hidden]) .detail-panel {
  transform: translateX(0);
}

.detail-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 12px;
  padding: 24px 28px 0;
  flex-shrink: 0;
}
.detail-title-area { flex: 1; min-width: 0; }
.detail-number {
  font-family: var(--font-mono);
  font-size: 12px;
  color: var(--text-3);
  display: block;
  margin-bottom: 4px;
}
.detail-title {
  font-size: 18px;
  font-weight: 700;
  letter-spacing: -0.3px;
  line-height: 1.3;
  color: var(--text-1);
}
.detail-header-right {
  display: flex;
  flex-direction: column;
  align-items: flex-end;
  gap: 10px;
  flex-shrink: 0;
}
.detail-badges { display: flex; gap: 6px; flex-wrap: wrap; justify-content: flex-end; }

.detail-close {
  width: 36px; height: 36px;
  border-radius: 50%;
  border: 1px solid var(--border);
  background: var(--surface);
  display: grid; place-items: center;
  color: var(--text-2);
  transition: all 0.2s;
}
.detail-close:hover { border-color: var(--red); color: var(--red); background: rgba(239,68,68,0.08); }

.detail-tabs {
  display: flex;
  gap: 4px;
  padding: 16px 28px 0;
  border-bottom: 1px solid var(--border-subtle);
  flex-shrink: 0;
}
.detail-tab {
  display: flex;
  align-items: center;
  gap: 7px;
  padding: 9px 18px;
  border-radius: var(--radius-sm) var(--radius-sm) 0 0;
  border: 1px solid transparent;
  border-bottom: none;
  font-size: 13px;
  font-weight: 500;
  color: var(--text-2);
  transition: all 0.2s;
  position: relative;
  bottom: -1px;
}
.detail-tab:hover { color: var(--text-1); }
.detail-tab.active {
  background: var(--bg-0);
  border-color: var(--border-subtle);
  border-bottom-color: var(--bg-0);
  color: var(--cyan);
}

.detail-body {
  flex: 1;
  overflow-y: auto;
  padding: 28px;
}
.detail-body::-webkit-scrollbar { width: 6px; }
.detail-body::-webkit-scrollbar-track { background: transparent; }
.detail-body::-webkit-scrollbar-thumb { background: var(--border); border-radius: 99px; }

/* Problem statement */
.problem-html { font-size: 14px; line-height: 1.75; color: var(--text-1); }
.problem-html p { margin-bottom: 12px; }
.problem-html pre {
  background: var(--bg-0);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius);
  padding: 14px 16px;
  margin: 14px 0;
  font-family: var(--font-mono);
  font-size: 13px;
  overflow-x: auto;
  color: var(--text-1);
  white-space: pre-wrap;
}
.problem-html code {
  font-family: var(--font-mono);
  font-size: 13px;
  background: var(--bg-3);
  padding: 1px 5px;
  border-radius: 4px;
  color: var(--cyan);
}
.problem-html ul, .problem-html ol { padding-left: 20px; margin-bottom: 12px; }
.problem-html li { margin-bottom: 4px; }
.problem-html strong { color: var(--text-1); font-weight: 600; }
.problem-html sup { font-size: 0.75em; }

/* Code block in solution tab */
.solution-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 14px;
  flex-wrap: wrap;
  gap: 10px;
}
.solution-lang-tabs { display: flex; gap: 6px; flex-wrap: wrap; }
.solution-lang-tab {
  padding: 5px 14px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border);
  background: var(--surface);
  font-family: var(--font-mono);
  font-size: 12px;
  font-weight: 600;
  color: var(--text-2);
  transition: all 0.2s;
  cursor: pointer;
}
.solution-lang-tab.active {
  border-color: var(--cyan);
  color: var(--cyan);
  background: var(--cyan-dim);
}
.solution-lang-tab:hover:not(.active) { border-color: var(--border-strong); }

.copy-btn {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 6px 14px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border);
  background: var(--surface);
  font-size: 12px;
  font-weight: 600;
  color: var(--text-2);
  transition: all 0.2s;
}
.copy-btn:hover { border-color: var(--green); color: var(--green); }
.copy-btn.copied { border-color: var(--green); color: var(--green); background: rgba(34,197,94,0.08); }

.code-wrap {
  border-radius: var(--radius);
  overflow: hidden;
  border: 1px solid var(--border-subtle);
}
.code-wrap pre { margin: 0 !important; border-radius: 0; border: none !important; }
.code-wrap pre code { font-size: 13px !important; line-height: 1.6; }

.solution-loading {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 12px;
  padding: 60px 20px;
  color: var(--text-3);
}

.detail-topic-chip {
  font-size: 11px;
  padding: 2px 8px;
  border-radius: 99px;
  background: var(--purple-dim);
  color: var(--purple);
  border: 1px solid rgba(168,85,247,0.2);
}
.leetcode-link {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  margin-bottom: 20px;
  font-size: 13px;
  color: var(--cyan);
  border-bottom: 1px solid transparent;
  transition: border-color 0.2s;
}
.leetcode-link:hover { border-color: var(--cyan); }

/* ── Scrollbar (global) ─────────────────────────────────────── */
body::-webkit-scrollbar { width: 8px; }
body::-webkit-scrollbar-track { background: var(--bg-0); }
body::-webkit-scrollbar-thumb { background: var(--bg-3); border-radius: 99px; }
body::-webkit-scrollbar-thumb:hover { background: var(--border-strong); }

/* ── Utilities ──────────────────────────────────────────────── */
.visually-hidden {
  position: absolute;
  width: 1px; height: 1px;
  margin: -1px; padding: 0;
  overflow: hidden; clip: rect(0,0,0,0);
  border: 0;
}

/* ── Responsive ─────────────────────────────────────────────── */
@media (max-width: 640px) {
  .hero-counters { flex-direction: column; gap: 12px; padding: 20px; }
  .hero-counter-divider { display: none; }
  .filters-bar { position: static; }
  .detail-header { padding: 18px 18px 0; }
  .detail-tabs { padding: 12px 18px 0; }
  .detail-body { padding: 18px; }
}

@media (max-width: 480px) {
  .problems-grid { grid-template-columns: 1fr; }
  .stats-grid { grid-template-columns: 1fr; }
}