:root {
  --bg: #0b1020;
  --bg-2: #111a33;
  --panel: rgba(255, 255, 255, 0.06);
  --panel-border: rgba(255, 255, 255, 0.10);
  --text: #eef2ff;
  --muted: #9aa5c4;
  --accent: #7c9cff;
  --accent-2: #5ee6c1;
  --accent-grad: linear-gradient(135deg, #7c9cff 0%, #5ee6c1 100%);
  --danger: #ff7c9c;
  --radius: 18px;
  --radius-sm: 12px;
  --shadow: 0 20px 60px rgba(0, 0, 0, 0.45);
  --ease: cubic-bezier(0.22, 1, 0.36, 1);
  --tile-gap: 4px;
}

* { box-sizing: border-box; }
html, body { height: 100%; }
body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Inter", "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  color: var(--text);
  background: radial-gradient(1200px 800px at 10% -10%, #1c2a5e 0%, transparent 60%),
              radial-gradient(900px 700px at 100% 110%, #0e3d3a 0%, transparent 60%),
              linear-gradient(180deg, var(--bg) 0%, var(--bg-2) 100%);
  background-attachment: fixed;
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  overflow-x: hidden;
}
.bg-glow {
  position: fixed; inset: 0; pointer-events: none; z-index: 0;
  background: radial-gradient(600px 400px at 70% 20%, rgba(124, 156, 255, 0.10), transparent 70%);
  animation: drift 18s ease-in-out infinite alternate;
}
@keyframes drift { from { transform: translate(0, 0); } to { transform: translate(-6%, 4%); } }

button { font: inherit; color: inherit; cursor: pointer; }
a { color: inherit; text-decoration: none; }

/* ---------- top bar ---------- */
.topbar {
  position: sticky; top: 0; z-index: 20;
  display: flex; align-items: center; justify-content: space-between;
  padding: 14px clamp(16px, 4vw, 40px);
  backdrop-filter: blur(14px); -webkit-backdrop-filter: blur(14px);
  background: rgba(11, 16, 32, 0.55);
  border-bottom: 1px solid var(--panel-border);
}
.brand { display: flex; align-items: center; gap: 10px; font-weight: 700; font-size: 1.1rem; letter-spacing: 0.2px; }
.brand-mark { font-size: 1.3rem; }
.topbar-link { color: var(--muted); font-size: 0.9rem; transition: color .2s; background: none; border: 0; padding: 6px 0; font: inherit; font-size: 0.9rem; cursor: pointer; }
.topbar-link[hidden] { display: none; }
.topbar-link:hover { color: var(--text); }

/* ---------- screens ---------- */
.screen { display: none; position: relative; z-index: 1; padding: clamp(16px, 4vw, 40px); max-width: 1200px; margin: 0 auto; }
.screen.active { display: block; animation: fadeIn .45s var(--ease); }
@keyframes fadeIn { from { opacity: 0; transform: translateY(8px); } to { opacity: 1; transform: none; } }

.panel {
  background: var(--panel);
  border: 1px solid var(--panel-border);
  border-radius: var(--radius);
  backdrop-filter: blur(10px); -webkit-backdrop-filter: blur(10px);
}

/* ---------- hero ---------- */
.hero { text-align: center; padding: 24px 0 28px; }
.hero h1 {
  margin: 0 0 10px; font-size: clamp(1.8rem, 4.5vw, 3rem); font-weight: 800; letter-spacing: -0.02em;
  background: var(--accent-grad); -webkit-background-clip: text; background-clip: text; color: transparent;
}
.hero p { margin: 0; color: var(--muted); font-size: 1.05rem; }

/* ---------- controls ---------- */
.controls {
  display: flex; flex-wrap: wrap; gap: 16px; align-items: center; justify-content: space-between;
  padding: 14px 16px; margin-bottom: 20px;
}
.controls-right { display: flex; flex-wrap: wrap; gap: 12px; align-items: center; }

.size-picker { display: flex; gap: 8px; }
.size-btn {
  display: flex; flex-direction: column; align-items: center; gap: 4px;
  padding: 10px 16px; border-radius: var(--radius-sm);
  background: transparent; border: 1px solid transparent;
  transition: background .25s, border-color .25s, transform .25s var(--ease);
}
.size-btn:hover { background: rgba(255,255,255,0.05); transform: translateY(-1px); }
.size-btn[aria-checked="true"] { background: rgba(124,156,255,0.16); border-color: rgba(124,156,255,0.5); }
.size-label { font-weight: 700; }
.size-sub { font-size: 0.72rem; color: var(--muted); text-transform: uppercase; letter-spacing: .08em; }
.size-grid { width: 30px; height: 30px; display: grid; gap: 2px; }
.size-btn[data-size="3"] .size-grid { grid-template-columns: repeat(3, 1fr); }
.size-btn[data-size="4"] .size-grid { grid-template-columns: repeat(4, 1fr); }
.size-btn[data-size="5"] .size-grid { grid-template-columns: repeat(5, 1fr); }
.size-grid i { display: block; background: currentColor; opacity: .55; border-radius: 2px; }
.size-grid i:last-child { opacity: .12; }

.filter-tabs { display: flex; gap: 4px; padding: 4px; border-radius: 999px; background: rgba(0,0,0,0.25); }
.tab { padding: 6px 14px; border-radius: 999px; border: 0; background: transparent; color: var(--muted); transition: all .25s; font-size: .9rem; }
.tab.active { background: rgba(255,255,255,0.12); color: var(--text); }
.tab:hover:not(.active) { color: var(--text); }

.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 6px;
  padding: 10px 18px; border-radius: 999px; border: 1px solid transparent;
  font-weight: 600; font-size: .95rem; white-space: nowrap;
  transition: transform .2s var(--ease), box-shadow .25s, background .25s, opacity .25s;
}
.btn:active { transform: scale(.97); }
.btn-primary { background: var(--accent-grad); color: #0b1020; box-shadow: 0 8px 24px rgba(94, 230, 193, 0.25); }
.btn-primary:hover { transform: translateY(-1px); box-shadow: 0 12px 30px rgba(94, 230, 193, 0.35); }
.btn-secondary { background: rgba(255,255,255,0.08); border-color: var(--panel-border); }
.btn-secondary:hover { background: rgba(255,255,255,0.14); }
.btn-ghost { background: transparent; color: var(--muted); padding-left: 6px; }
.btn-ghost:hover { color: var(--text); }
.toggle[aria-pressed="true"] { background: rgba(124,156,255,0.22); border-color: rgba(124,156,255,0.5); }

/* ---------- gallery ---------- */
.gallery {
  display: grid; gap: 14px;
  grid-template-columns: repeat(auto-fill, minmax(150px, 1fr));
}
.card {
  position: relative; aspect-ratio: 1; border-radius: var(--radius-sm); overflow: hidden;
  padding: 0; border: 1px solid var(--panel-border); background: var(--panel);
  transition: transform .35s var(--ease), box-shadow .35s;
  animation: cardIn .5s var(--ease) both;
}
@keyframes cardIn { from { opacity: 0; transform: scale(.94); } to { opacity: 1; transform: none; } }
.card img { width: 100%; height: 100%; object-fit: cover; display: block; transition: transform .6s var(--ease); }
.card:hover { transform: translateY(-4px); box-shadow: var(--shadow); }
.card:hover img { transform: scale(1.06); }
.card .card-label {
  position: absolute; left: 0; right: 0; bottom: 0; padding: 22px 12px 10px;
  text-align: left; font-size: .85rem; font-weight: 600;
  background: linear-gradient(to top, rgba(0,0,0,.75), transparent);
}
.card .badge {
  position: absolute; top: 8px; right: 8px; font-size: .7rem; font-weight: 700;
  padding: 3px 8px; border-radius: 999px; background: rgba(94,230,193,.9); color: #0b1020;
}
.card.hidden { display: none; }

/* ---------- game layout ---------- */
.game-layout { display: grid; grid-template-columns: 280px 1fr; gap: 24px; align-items: start; }
.side { padding: 18px; display: flex; flex-direction: column; gap: 16px; position: sticky; top: 84px; }
.back { align-self: flex-start; }
.preview-wrap { border-radius: var(--radius-sm); overflow: hidden; border: 1px solid var(--panel-border); }
.preview { width: 100%; aspect-ratio: 1; object-fit: cover; display: block; }
.preview-caption { display: flex; justify-content: space-between; padding: 8px 12px; font-size: .85rem; background: rgba(0,0,0,.3); }
.preview-caption span:last-child { color: var(--muted); }
.preview-credit { display: block; padding: 6px 12px 8px; font-size: .72rem; color: var(--muted); background: rgba(0,0,0,.3); line-height: 1.35; transition: color .2s; }
.preview-credit:hover { color: var(--text); text-decoration: underline; }
.footnote { margin: 28px 0 8px; text-align: center; font-size: .78rem; color: var(--muted); }
.footnote a { text-decoration: underline; }

.stats { display: grid; grid-template-columns: repeat(3, 1fr); gap: 8px; }
.stat { display: flex; flex-direction: column; align-items: center; padding: 10px 6px; border-radius: var(--radius-sm); background: rgba(0,0,0,.25); }
.stat-value { font-size: 1.3rem; font-weight: 800; font-variant-numeric: tabular-nums; }
.stat-key { font-size: .7rem; color: var(--muted); text-transform: uppercase; letter-spacing: .08em; }
.side-actions { display: flex; flex-direction: column; gap: 8px; }
.hint-text { margin: 0; font-size: .8rem; color: var(--muted); line-height: 1.45; }

.board-wrap { display: flex; justify-content: center; align-items: flex-start; }
.board {
  --n: 4;
  position: relative;
  width: min(100%, calc(100vh - 140px), 720px);
  aspect-ratio: 1;
  padding: var(--tile-gap);
  border-radius: var(--radius);
  background: rgba(0,0,0,.35);
  border: 1px solid var(--panel-border);
  box-shadow: var(--shadow);
  outline: none;
  touch-action: none;
  user-select: none; -webkit-user-select: none;
}
.board:focus-visible { box-shadow: var(--shadow), 0 0 0 3px rgba(124,156,255,.6); }
.board-inner { position: absolute; inset: var(--tile-gap); }

.tile {
  transition: transform .28s var(--ease), padding .6s var(--ease);
  position: absolute; left: 0; top: 0;
  width: calc(100% / var(--n));
  height: calc(100% / var(--n));
  padding: calc(var(--tile-gap) / 2);
  transition: transform .28s var(--ease);
  will-change: transform;
  cursor: pointer;
}
.tile-face {
  width: 100%; height: 100%; border-radius: 10px;
  background-image: var(--img);
  background-size: calc(var(--n) * 100%) calc(var(--n) * 100%);
  background-position: var(--bx) var(--by);
  box-shadow: inset 0 0 0 1px rgba(255,255,255,.08), 0 6px 14px rgba(0,0,0,.35);
  transition: transform .2s var(--ease), box-shadow .2s, border-radius .6s var(--ease);
  display: flex; align-items: flex-start; justify-content: flex-start;
}
.tile.movable:hover .tile-face { transform: scale(1.025); box-shadow: inset 0 0 0 1px rgba(255,255,255,.25), 0 10px 22px rgba(0,0,0,.45); }
.tile.pressed .tile-face { transform: scale(.96); }
.tile-num {
  margin: 6px; padding: 2px 8px; border-radius: 999px;
  background: rgba(0,0,0,.55); font-size: .8rem; font-weight: 700;
  opacity: 0; transition: opacity .25s;
  backdrop-filter: blur(4px);
}
.board.show-numbers .tile-num { opacity: 1; }
.tile.empty { opacity: 0; pointer-events: none; transition: transform .28s var(--ease), opacity .6s ease .35s; }
.tile.wrong .tile-face { }

/* solved state: seamless picture */
.board.solved .tile { pointer-events: none; padding: 0; transition: transform .28s var(--ease), padding .6s var(--ease); }
.board.solved .tile.empty { opacity: 1; }
.board.solved .tile-face { border-radius: 0; box-shadow: none; transform: none; }
.board.solved .tile-num { opacity: 0; }
.board.solved { animation: pulse .8s var(--ease); }
@keyframes pulse { 0% { box-shadow: var(--shadow); } 40% { box-shadow: 0 0 0 10px rgba(94,230,193,.35), var(--shadow); } 100% { box-shadow: var(--shadow); } }

/* shuffle animation */
.board.shuffling .tile { transition: transform .5s var(--ease); }

/* ---------- win overlay ---------- */
.overlay {
  position: fixed; inset: 0; z-index: 30;
  display: flex; align-items: center; justify-content: center;
  background: rgba(5, 8, 18, .6); backdrop-filter: blur(6px);
  opacity: 0; pointer-events: none; transition: opacity .4s;
}
.overlay.show { opacity: 1; pointer-events: auto; }
.win-card {
  position: relative; overflow: hidden; text-align: center; padding: 36px 40px; max-width: 420px; width: calc(100% - 32px);
  background: rgba(17, 26, 51, .92);
  transform: translateY(20px) scale(.96); transition: transform .5s var(--ease);
}
.overlay.show .win-card { transform: none; }
.win-emoji { font-size: 3rem; animation: bounce 1s var(--ease) infinite alternate; }
@keyframes bounce { from { transform: translateY(0); } to { transform: translateY(-8px); } }
.win-card h2 { margin: 6px 0 8px; font-size: 2rem; letter-spacing: -0.02em; }
.win-card p { margin: 0; color: var(--muted); }
.win-record { margin-top: 6px !important; color: var(--accent-2) !important; font-weight: 700; min-height: 1.3em; }
.win-actions { display: flex; gap: 10px; justify-content: center; margin-top: 22px; flex-wrap: wrap; }

.confetti { position: absolute; inset: 0; pointer-events: none; }
.confetti i {
  position: absolute; top: -12px; width: 8px; height: 14px; border-radius: 2px;
  animation: fall linear forwards;
}
@keyframes fall {
  0% { transform: translateY(0) rotate(0deg); opacity: 1; }
  100% { transform: translateY(520px) rotate(720deg); opacity: 0; }
}

/* ---------- responsive ---------- */
@media (max-width: 860px) {
  .game-layout { grid-template-columns: 1fr; }
  .side { position: static; order: 2; }
  .board-wrap { order: 1; }
  .board { width: min(100%, calc(100vh - 220px)); }
  .preview-wrap { display: grid; grid-template-columns: 90px 1fr; align-items: center; }
  .preview { width: 90px; }
  .preview-caption { flex-direction: column; gap: 2px; background: transparent; }
  .preview-credit { grid-column: 1 / -1; background: transparent; padding-top: 0; }
  .side-actions { flex-direction: row; flex-wrap: wrap; }
  .side-actions .btn { flex: 1; }
}
@media (max-width: 520px) {
  .controls { padding: 12px; }
  .size-btn { padding: 8px 10px; }
  .gallery { grid-template-columns: repeat(auto-fill, minmax(120px, 1fr)); gap: 10px; }
  .hero h1 { font-size: 1.7rem; }
}
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation: none !important; transition-duration: .01ms !important; }
}
.glyph { font-weight: 800; opacity: .85; }