/* =====================================================================
   Sudoku — sleek glass design
   Light & dark themes via CSS variables on html[data-theme].
   ===================================================================== */

/* ================= Themes ================= */
:root,
html[data-theme="light"] {
  --bg: #eef1f8;
  --bg-grad: linear-gradient(180deg, #f4f6fb 0%, #e9edf6 100%);
  --glow-a: rgba(99, 102, 241, 0.32);
  --glow-b: rgba(56, 189, 248, 0.28);

  --surface: rgba(255, 255, 255, 0.66);
  --surface-strong: rgba(255, 255, 255, 0.88);
  --surface-2: rgba(15, 23, 42, 0.045);
  --glass-border: rgba(255, 255, 255, 0.65);

  --text: #0f172a;
  --muted: #64748b;

  --accent: #4f46e5;
  --accent-2: #7c3aed;
  --btn-grad: linear-gradient(135deg, #4f46e5, #7c3aed);
  --accent-glow: rgba(79, 70, 229, 0.35);
  --accent-text: #ffffff;
  --link: #4f46e5;

  --board-line: rgba(15, 23, 42, 0.14);
  --thick-line: #3f4a5f;
  --cell-bg: rgba(255, 255, 255, 0.72);
  --given-bg: rgba(15, 23, 42, 0.035);
  --cell-hover-filter: brightness(0.97);
  --given: #0f172a;
  --entry: #4338ca;
  --candidate: #94a3b8;

  --hl: rgba(99, 102, 241, 0.14);
  --selected: rgba(99, 102, 241, 0.32);
  --conflict-bg: rgba(245, 158, 11, 0.28);
  --error-bg: rgba(239, 68, 68, 0.18);
  --error: #dc2626;

  --shine: rgba(255, 255, 255, 0.9);
  --shine-soft: rgba(255, 255, 255, 0.55);

  --overlay: rgba(15, 23, 42, 0.38);
  --shadow-sm: 0 1px 2px rgba(15, 23, 42, 0.05), 0 1px 3px rgba(15, 23, 42, 0.07);
  --shadow-md: 0 4px 14px rgba(15, 23, 42, 0.08), 0 2px 4px rgba(15, 23, 42, 0.05);
  --shadow-lg: 0 20px 44px rgba(15, 23, 42, 0.14), 0 6px 16px rgba(15, 23, 42, 0.08);
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 16px;
}

html[data-theme="dark"] {
  --bg: #0a0f1e;
  --bg-grad: linear-gradient(180deg, #0d1424 0%, #080d1a 100%);
  --glow-a: rgba(99, 102, 241, 0.28);
  --glow-b: rgba(59, 130, 246, 0.22);

  --surface: rgba(255, 255, 255, 0.055);
  --surface-strong: rgba(17, 24, 39, 0.88);
  --surface-2: rgba(255, 255, 255, 0.06);
  --glass-border: rgba(255, 255, 255, 0.12);

  --text: #e2e8f0;
  --muted: #94a3b8;

  --accent: #818cf8;
  --accent-2: #a78bfa;
  --btn-grad: linear-gradient(135deg, #6366f1, #8b5cf6);
  --accent-glow: rgba(129, 140, 248, 0.35);
  --accent-text: #ffffff;
  --link: #a5b4fc;

  --board-line: rgba(148, 163, 184, 0.2);
  --thick-line: #8ea0b8;
  --cell-bg: rgba(13, 20, 36, 0.55);
  --given-bg: rgba(255, 255, 255, 0.05);
  --cell-hover-filter: brightness(1.18);
  --given: #f1f5f9;
  --entry: #a5b4fc;
  --candidate: #7e8ea6;

  --hl: rgba(129, 140, 248, 0.18);
  --selected: rgba(129, 140, 248, 0.36);
  --conflict-bg: rgba(245, 158, 11, 0.22);
  --error-bg: rgba(239, 68, 68, 0.22);
  --error: #f87171;

  --shine: rgba(255, 255, 255, 0.16);
  --shine-soft: rgba(255, 255, 255, 0.05);

  --overlay: rgba(3, 7, 18, 0.66);
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.35);
  --shadow-md: 0 6px 18px rgba(0, 0, 0, 0.4);
  --shadow-lg: 0 22px 48px rgba(0, 0, 0, 0.55);
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 16px;
}

/* ================= Base ================= */
* { box-sizing: border-box; }

html, body { margin: 0; min-height: 100%; }

body {
  font-family: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  background: var(--bg-grad);
  color: var(--text);
  transition: background 0.25s ease, color 0.25s ease;
  min-height: 100vh;
}

.view {
  position: relative;
  z-index: 1;
  max-width: 900px;
  margin: 0 auto;
  padding: 16px;
}

/* Zoom level: scales in-flow content + modal boxes so the whole UI
   grows together without affecting fixed-position backdrops. */
html { --zoom: 1; }
.view,
.modal-box { zoom: var(--zoom); }

.hidden { display: none !important; }

h1, h2 { margin: 0 0 8px; }
h2 { font-size: 1.05rem; font-weight: 700; letter-spacing: -0.01em; }
em { font-style: normal; font-weight: 600; color: var(--link); }

.sub { font-size: 0.8rem; color: var(--muted); }
.hint { font-size: 0.8rem; color: var(--muted); margin: 8px 0 0; line-height: 1.5; }

/* ================= Ambient background glows ================= */
.bg-glow {
  position: fixed;
  inset: 0;
  z-index: 0;
  overflow: hidden;
  pointer-events: none;
}

.glow {
  position: absolute;
  border-radius: 50%;
  filter: blur(90px);
  opacity: 0.9;
}

.glow-1 {
  width: 520px;
  height: 520px;
  top: -160px;
  right: -120px;
  background: radial-gradient(circle, var(--glow-a) 0%, transparent 70%);
}

.glow-2 {
  width: 460px;
  height: 460px;
  bottom: -180px;
  left: -140px;
  background: radial-gradient(circle, var(--glow-b) 0%, transparent 70%);
}

/* ================= Buttons ================= */
button {
  font: inherit;
  color: var(--text);
  background: var(--surface);
  border: 1px solid var(--glass-border);
  border-radius: var(--radius-sm);
  padding: 8px 14px;
  cursor: pointer;
  box-shadow: inset 0 1px 0 var(--shine), var(--shadow-sm);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  transition: background 0.15s ease, box-shadow 0.15s ease, color 0.15s ease,
    border-color 0.15s ease, transform 0.06s ease;
}

button:hover {
  background: var(--surface-strong);
  border-color: var(--accent);
  color: var(--link);
  box-shadow: inset 0 1px 0 var(--shine), var(--shadow-md);
}

button:active { transform: scale(0.97); }

button:disabled {
  opacity: 0.45;
  cursor: not-allowed;
  background: var(--surface);
  color: var(--muted);
  box-shadow: none;
}

button:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

button.primary {
  background: var(--btn-grad);
  color: var(--accent-text);
  border-color: transparent;
  font-weight: 600;
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.25), 0 4px 14px var(--accent-glow);
}

button.primary:hover {
  background: var(--btn-grad);
  color: var(--accent-text);
  border-color: transparent;
  transform: translateY(-1px);
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.25), 0 8px 20px var(--accent-glow);
}

/* ================= Header ================= */
.app-header {
  position: sticky;
  top: 0;
  z-index: 6;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin: -16px -16px 20px;
  padding: 12px 16px;
  background: var(--surface);
  backdrop-filter: blur(14px) saturate(150%);
  -webkit-backdrop-filter: blur(14px) saturate(150%);
  border-bottom: 1px solid var(--glass-border);
  box-shadow: inset 0 1px 0 var(--shine), var(--shadow-sm);
}

.logo {
  margin: 0;
  font-size: 1.5rem;
  font-weight: 800;
  letter-spacing: -0.02em;
  background: var(--btn-grad);
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}

.game-title { text-align: center; line-height: 1.25; }
.game-title #game-difficulty-label { font-weight: 700; }

.header-controls {
  display: flex;
  align-items: center;
  gap: 8px;
}

.timer {
  display: inline-flex;
  align-items: center;
  gap: 7px;
  font-variant-numeric: tabular-nums;
  font-weight: 600;
  padding: 6px 12px;
  background: var(--surface-2);
  border: 1px solid var(--glass-border);
  border-radius: 999px;
  box-shadow: inset 0 1px 0 var(--shine);
}

.timer::before {
  content: "";
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-glow);
}

.icon-btn { font-size: 1.05rem; padding: 6px 10px; }

/* ================= Cards (home) ================= */
.home-body { display: flex; flex-direction: column; gap: 14px; }

.card {
  position: relative;
  overflow: hidden;
  background: var(--surface);
  backdrop-filter: blur(14px) saturate(150%);
  -webkit-backdrop-filter: blur(14px) saturate(150%);
  border: 1px solid var(--glass-border);
  border-radius: var(--radius-md);
  padding: 18px;
  box-shadow: inset 0 1px 0 var(--shine), var(--shadow-md);
}

/* Glass shine: crisp top hairline + soft downward sheen. */
.card::before {
  content: "";
  position: absolute;
  top: 0;
  left: 10%;
  right: 10%;
  height: 1px;
  background: linear-gradient(90deg, transparent, var(--shine), transparent);
  pointer-events: none;
}

.card::after {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 45%;
  background: linear-gradient(180deg, var(--shine-soft), transparent);
  pointer-events: none;
}

.difficulty-buttons { display: flex; gap: 10px; margin-top: 12px; }

.diff-btn {
  flex: 1;
  padding: 13px;
  font-size: 1rem;
  font-weight: 600;
  background: var(--btn-grad);
  color: var(--accent-text);
  border-color: transparent;
  border-radius: 10px;
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.22), 0 4px 14px var(--accent-glow);
}

.diff-btn:hover {
  background: var(--btn-grad);
  color: var(--accent-text);
  transform: translateY(-1px);
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.22), 0 8px 22px var(--accent-glow);
}

.toggle-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 16px;
  padding: 10px 0;
  cursor: pointer;
  border-bottom: 1px solid var(--glass-border);
}

.toggle-row:last-child { border-bottom: none; }

.toggle-row input {
  width: 18px;
  height: 18px;
  accent-color: var(--accent);
  cursor: pointer;
}

.zoom-control {
  display: flex;
  align-items: center;
  gap: 8px;
}

.zoom-btn {
  width: 34px;
  height: 34px;
  padding: 0;
  font-size: 1.1rem;
  font-weight: 600;
  line-height: 1;
  display: inline-flex;
  align-items: center;
  justify-content: center;
}

.zoom-label {
  min-width: 52px;
  text-align: center;
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--muted);
  font-variant-numeric: tabular-nums;
}

.zoom-header .zoom-btn { width: 30px; height: 30px; font-size: 1rem; }
.zoom-header .zoom-label { min-width: 44px; }

/* ================= Lists ================= */
.game-list { list-style: none; margin: 0; padding: 0; }

.game-list li {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
  padding: 11px 0;
  border-bottom: 1px solid var(--glass-border);
}

.game-list li:last-child { border-bottom: none; }

/* ~5 visible rows, rest scrolled. */
.game-list.scrollable {
  max-height: 260px;
  overflow-y: auto;
  padding-right: 6px;
  scrollbar-width: thin;
  scrollbar-color: var(--muted) transparent;
}

.game-list.scrollable::-webkit-scrollbar { width: 8px; }
.game-list.scrollable::-webkit-scrollbar-track { background: transparent; }
.game-list.scrollable::-webkit-scrollbar-thumb {
  background: color-mix(in srgb, var(--muted) 55%, transparent);
  border-radius: 4px;
}

.row-actions { display: flex; gap: 6px; flex-shrink: 0; }

/* ================= Stats ================= */
.stats {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(130px, 1fr));
  gap: 10px;
  margin-top: 8px;
}

.stat {
  position: relative;
  overflow: hidden;
  background: var(--surface-2);
  border: 1px solid var(--glass-border);
  border-radius: 10px;
  padding: 12px 8px;
  text-align: center;
  box-shadow: inset 0 1px 0 var(--shine);
}

.stat .num {
  font-size: 1.3rem;
  font-weight: 700;
  letter-spacing: -0.02em;
}

.stat .label { font-size: 0.74rem; color: var(--muted); margin-top: 2px; }

/* ================= Board ================= */
.game-body {
  display: flex;
  flex-direction: column;
  gap: 18px;
  align-items: center;
}

.board-wrap { position: relative; }

.board {
  display: grid;
  grid-template-columns: repeat(9, 1fr);
  width: min(92vw, 520px);
  background: var(--cell-bg);
  border: 2px solid var(--thick-line);
  border-radius: 10px;
  overflow: hidden;
  box-shadow: var(--shadow-lg), inset 0 1px 0 var(--shine);
}

.cell {
  position: relative;
  aspect-ratio: 1;
  background: var(--cell-bg);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  user-select: none;
  transition: background 0.1s ease, filter 0.1s ease;
}

.cell.has-r { border-right: 1px solid var(--board-line); }
.cell.has-b { border-bottom: 1px solid var(--board-line); }
.cell.thick-r { border-right: 2px solid var(--thick-line); }
.cell.thick-b { border-bottom: 2px solid var(--thick-line); }

.cell:not(.given):not(.filled):not(.selected):not(.hl):not(.error):not(.conflict):hover {
  filter: var(--cell-hover-filter);
}

.cell.given { background: var(--given-bg); }
.cell.hl { background: var(--hl); }
.cell.selected { background: var(--selected); }
.cell.conflict { background: var(--conflict-bg); }
.cell.error { background: var(--error-bg); }

.cell .value {
  font-size: clamp(16px, 4.5vw, 26px);
  font-weight: 600;
  line-height: 1;
}

.cell.given .value { color: var(--given); font-weight: 700; }
.cell.filled .value { color: var(--entry); font-weight: 600; }
.cell.error .value { color: var(--error); font-weight: 700; }

.cand-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  width: 100%;
  height: 100%;
  padding: 1px;
  font-size: clamp(9px, 1.8vw, 11px);
  line-height: 1;
  color: var(--candidate);
}

.cand-grid span {
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 500;
}

.cand-grid .single {
  grid-column: 1 / -1;
  font-size: clamp(11px, 2.3vw, 14px);
  font-weight: 500;
}

/* ================= Controls ================= */
.controls {
  display: flex;
  flex-direction: column;
  gap: 12px;
  width: min(92vw, 520px);
}

.mode-toggle { display: flex; gap: 8px; justify-content: center; }

.mode-btn { flex: 1; max-width: 180px; }

.mode-btn.active {
  background: var(--btn-grad);
  color: var(--accent-text);
  border-color: transparent;
  font-weight: 600;
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.22), 0 4px 14px var(--accent-glow);
}

.mode-btn.active:hover {
  background: var(--btn-grad);
  color: var(--accent-text);
}

.number-pad {
  display: grid;
  grid-template-columns: repeat(9, 1fr);
  gap: 6px;
}

.pad-btn {
  aspect-ratio: 1;
  font-size: clamp(14px, 4vw, 20px);
  font-weight: 600;
  border-radius: 10px;
}

.pad-btn:hover {
  background: var(--surface-strong);
  border-color: var(--accent);
  color: var(--link);
  transform: translateY(-1px);
}

.pad-btn:active { transform: scale(0.94); }

/* A digit fully placed (all 9 instances) is no longer in play. */
.pad-btn:disabled {
  opacity: 0.35;
  color: var(--muted);
  text-decoration: line-through;
  text-decoration-thickness: 1px;
  box-shadow: none;
}

/* Highlights the pad numbers already set in the selected cell. */
.pad-btn.pad-active {
  background: var(--selected);
  border-color: var(--accent);
  color: var(--accent);
  box-shadow: inset 0 1px 0 var(--shine);
}

.pad-btn.pad-active:hover {
  background: var(--selected);
  border-color: var(--accent);
  color: var(--accent);
}

.action-buttons { display: flex; gap: 8px; justify-content: center; }
.action-buttons button { flex: 1; max-width: 180px; }

/* ================= Overlay / Modals ================= */
.overlay,
.modal {
  position: fixed;
  inset: 0;
  background: var(--overlay);
  backdrop-filter: blur(5px);
  -webkit-backdrop-filter: blur(5px);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 10;
}

.overlay { position: absolute; border-radius: 10px; z-index: 5; }

.overlay-box,
.modal-box {
  position: relative;
  overflow: hidden;
  background: var(--surface-strong);
  backdrop-filter: blur(20px) saturate(150%);
  -webkit-backdrop-filter: blur(20px) saturate(150%);
  border: 1px solid var(--glass-border);
  border-radius: var(--radius-md);
  padding: 26px;
  text-align: center;
  width: min(90vw, 320px);
  box-shadow: inset 0 1px 0 var(--shine), var(--shadow-lg);
}

.overlay-box::before,
.modal-box::before {
  content: "";
  position: absolute;
  top: 0;
  left: 10%;
  right: 10%;
  height: 1px;
  background: linear-gradient(90deg, transparent, var(--shine), transparent);
  pointer-events: none;
}

.overlay-box::after,
.modal-box::after {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 40%;
  background: linear-gradient(180deg, var(--shine-soft), transparent);
  pointer-events: none;
}

.stack {
  display: flex;
  flex-direction: column;
  gap: 8px;
  margin-top: 14px;
}

/* ================= Misc ================= */
::selection { background: var(--accent); color: var(--accent-text); }

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { transition: none !important; }
  button:active, button.primary:hover, .pad-btn:hover, .diff-btn:hover { transform: none; }
}