:root {
  --bg:           #0a0f1e;
  --bg-card:      #0f1729;
  --bg-elevated:  #151e35;
  --bg-hover:     #1a2540;

  --border:       #1e2d4a;
  --border-thick: #243555;

  --text:         #e2e8f8;
  --text-muted:   #5a6a88;
  --text-dim:     #3a4a66;

  --accent:       #3b82f6;
  --accent-glow:  rgba(59,130,246,0.18);
  --accent-soft:  rgba(59,130,246,0.10);

  --user-num:     #60a5fa;
  --given-num:    #e2e8f8;
  --note-num:     #4a7aaa;

  --error:        #ef4444;
  --error-bg:     rgba(239,68,68,0.15);

  --highlight-row: rgba(59,130,246,0.06);
  --highlight-sel: rgba(59,130,246,0.22);
  --highlight-same: rgba(96,165,250,0.13);

  --success:      #22c55e;
  --warning:      #f59e0b;

  --radius:       12px;
  --radius-sm:    7px;
  --shadow:       0 8px 32px rgba(0,0,0,0.5);
  --shadow-sm:    0 2px 10px rgba(0,0,0,0.3);

  --font-ui:      'Outfit', sans-serif;
  --font-mono:    'DM Mono', monospace;

  --cell-size:    min(52px, 9.5vw);
}

*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }

body {
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-ui);
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: flex-start;
  padding: 24px 16px 40px;
  overflow-x: hidden;
}

.bg-decoration {
  position: fixed;
  inset: 0;
  pointer-events: none;
  z-index: 0;
  overflow: hidden;
}

.bg-grid {
  position: absolute;
  inset: 0;
  background-image:
    linear-gradient(rgba(59,130,246,0.03) 1px, transparent 1px),
    linear-gradient(90deg, rgba(59,130,246,0.03) 1px, transparent 1px);
  background-size: 40px 40px;
}

.glow {
  position: absolute;
  border-radius: 50%;
  filter: blur(100px);
  opacity: 0.35;
}
.glow-1 {
  width: 500px; height: 500px;
  background: radial-gradient(circle, #1d4ed8, transparent 70%);
  top: -150px; left: -100px;
}
.glow-2 {
  width: 400px; height: 400px;
  background: radial-gradient(circle, #0f172a, #1e3a5f, transparent 70%);
  bottom: -100px; right: -80px;
}

.app-wrapper {
  position: relative;
  z-index: 1;
  width: 100%;
  max-width: 520px;
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0 4px;
}

.logo {
  display: flex;
  align-items: center;
  gap: 10px;
}

.logo-icon {
  font-size: 22px;
  color: var(--accent);
  filter: drop-shadow(0 0 8px var(--accent));
  animation: pulse-icon 3s ease-in-out infinite;
}

@keyframes pulse-icon {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.65; }
}

.logo-text {
  font-family: var(--font-mono);
  font-size: 20px;
  font-weight: 500;
  letter-spacing: 0.22em;
  color: var(--text);
}

.timer-box {
  display: flex;
  flex-direction: column;
  align-items: flex-end;
  gap: 1px;
}

.timer-label {
  font-family: var(--font-mono);
  font-size: 10px;
  letter-spacing: 0.18em;
  color: var(--text-muted);
}

.timer-display {
  font-family: var(--font-mono);
  font-size: 22px;
  font-weight: 400;
  color: var(--accent);
  letter-spacing: 0.06em;
  text-shadow: 0 0 20px var(--accent-glow);
}

.controls-bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 12px 16px;
  gap: 12px;
  flex-wrap: wrap;
}

.control-label {
  font-family: var(--font-mono);
  font-size: 9px;
  letter-spacing: 0.18em;
  color: var(--text-muted);
  display: block;
  margin-bottom: 6px;
}

.difficulty-buttons {
  display: flex;
  gap: 4px;
}

.diff-btn {
  font-family: var(--font-ui);
  font-size: 12px;
  font-weight: 500;
  padding: 5px 13px;
  border-radius: 6px;
  border: 1px solid var(--border-thick);
  background: transparent;
  color: var(--text-muted);
  cursor: pointer;
  transition: all 0.2s ease;
  letter-spacing: 0.02em;
}

.diff-btn:hover {
  background: var(--bg-hover);
  color: var(--text);
  border-color: var(--accent);
}

.diff-btn.active {
  background: var(--accent-soft);
  color: var(--accent);
  border-color: var(--accent);
  box-shadow: 0 0 12px var(--accent-glow);
}

.action-buttons {
  display: flex;
  gap: 6px;
  align-items: center;
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  font-family: var(--font-ui);
  font-size: 12px;
  font-weight: 500;
  padding: 7px 13px;
  border-radius: var(--radius-sm);
  border: 1px solid transparent;
  cursor: pointer;
  transition: all 0.18s ease;
  letter-spacing: 0.03em;
  white-space: nowrap;
}

.btn:active { transform: scale(0.96); }

.btn-primary {
  background: var(--accent);
  color: #fff;
  border-color: var(--accent);
  box-shadow: 0 0 16px rgba(59,130,246,0.3);
}
.btn-primary:hover {
  background: #2563eb;
  box-shadow: 0 0 24px rgba(59,130,246,0.45);
}

.btn-secondary {
  background: var(--bg-elevated);
  color: var(--text-muted);
  border-color: var(--border-thick);
}
.btn-secondary:hover {
  background: var(--bg-hover);
  color: var(--text);
  border-color: var(--accent);
}

.btn-wide { width: 100%; justify-content: center; padding: 12px; font-size: 14px; }

.stats-bar {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 10px 18px;
  flex-wrap: wrap;
  row-gap: 8px;
}

.stat {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 2px;
  padding: 0 18px;
}

.stat-val {
  font-family: var(--font-mono);
  font-size: 20px;
  font-weight: 400;
  color: var(--text);
  line-height: 1;
}

.stat-label {
  font-size: 9px;
  font-weight: 400;
  letter-spacing: 0.14em;
  color: var(--text-muted);
  text-transform: uppercase;
}

.stat-divider {
  width: 1px;
  height: 30px;
  background: var(--border-thick);
  flex-shrink: 0;
}

.toggle-row {
  flex-direction: row;
  gap: 8px;
  align-items: center;
}

.toggle-label {
  font-size: 11px;
  color: var(--text-muted);
  cursor: pointer;
  letter-spacing: 0.04em;
}

.toggle-switch { 
  position: relative; 
  display: inline-block; 
  width: 34px; 
  height: 18px; 
  z-index: 1;
}
.toggle-switch input { 
  opacity: 0; 
  width: 100%; 
  height: 100%; 
  position: absolute;
  z-index: 2;
  cursor: pointer;
  margin: 0;
}
.toggle-slider {
  position: absolute;
  inset: 0;
  background: var(--border-thick);
  border-radius: 18px;
  cursor: pointer;
  transition: 0.25s;
  pointer-events: none;
  z-index: 1;
}
.toggle-slider::before {
  content: '';
  position: absolute;
  width: 12px; height: 12px;
  left: 3px; top: 3px;
  background: var(--text-muted);
  border-radius: 50%;
  transition: 0.25s;
}
.toggle-switch input:checked + .toggle-slider { background: var(--accent); }
.toggle-switch input:checked + .toggle-slider::before {
  transform: translateX(16px);
  background: #fff;
}

.game-area {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 16px;
}

.grid-container {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 16px;
  box-shadow: var(--shadow);
}

.sudoku-grid {
  display: grid;
  grid-template-columns: repeat(9, var(--cell-size));
  grid-template-rows: repeat(9, var(--cell-size));
  border: 2.5px solid #3a5080;
  border-radius: 6px;
  overflow: hidden;
  position: relative;
}

.cell {
  width: var(--cell-size);
  height: var(--cell-size);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-mono);
  font-size: clamp(16px, 3.5vw, 22px);
  font-weight: 400;
  cursor: pointer;
  position: relative;
  border-right: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
  transition: background 0.12s ease, color 0.12s ease;
  user-select: none;
  outline: none;
}

.cell:nth-child(9n) { border-right: none; }
.cell:nth-child(n+73) { border-bottom: none; }

.cell:nth-child(9n+3),
.cell:nth-child(9n+6) {
  border-right: 2.5px solid #3a5080;
}

.cell:nth-child(n+19):nth-child(-n+27),
.cell:nth-child(n+46):nth-child(-n+54) {
  border-bottom: 2.5px solid #3a5080;
}

.cell:hover:not(.given):not(.selected) {
  background: var(--bg-hover);
}

.cell.highlighted { background: var(--highlight-row); }
.cell.same-num    { background: var(--highlight-same); }
.cell.selected    {
  background: var(--highlight-sel) !important;
  box-shadow: inset 0 0 0 2px var(--accent);
  z-index: 2;
}

.cell.given  { color: var(--given-num); }
.cell.user   { color: var(--user-num); }

.cell.error {
  background: var(--error-bg) !important;
  color: var(--error) !important;
  animation: shake 0.3s ease;
}

.cell.correct-flash {
  animation: flash-correct 0.4s ease;
}

@keyframes shake {
  0%,100% { transform: translateX(0); }
  25% { transform: translateX(-3px); }
  75% { transform: translateX(3px); }
}

@keyframes flash-correct {
  0% { background: rgba(34,197,94,0.3); }
  100% { background: transparent; }
}

@keyframes pop-in {
  0%   { transform: scale(0.7); opacity: 0; }
  70%  { transform: scale(1.1); }
  100% { transform: scale(1); opacity: 1; }
}

.cell .num-value {
  animation: pop-in 0.2s ease;
}

.notes-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, 1fr);
  width: 100%;
  height: 100%;
  padding: 2px;
}

.note-digit {
  font-family: var(--font-mono);
  font-size: clamp(7px, 1.5vw, 10px);
  color: var(--note-num);
  display: flex;
  align-items: center;
  justify-content: center;
  line-height: 1;
}

.note-digit.active { color: var(--accent); }

.cell.solving {
  animation: solve-pulse 0.35s ease;
}

@keyframes solve-pulse {
  0%   { background: rgba(59,130,246,0.35); }
  100% { background: transparent; }
}

.numpad {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 7px;
  width: 100%;
  max-width: 380px;
}

.num-btn {
  font-family: var(--font-mono);
  font-size: clamp(18px, 4vw, 24px);
  font-weight: 400;
  height: clamp(44px, 10vw, 54px);
  background: var(--bg-card);
  color: var(--user-num);
  border: 1px solid var(--border-thick);
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all 0.15s ease;
  display: flex;
  align-items: center;
  justify-content: center;
  position: relative;
  overflow: hidden;
}

.num-btn::after {
  content: '';
  position: absolute;
  inset: 0;
  background: var(--accent);
  opacity: 0;
  transition: opacity 0.15s;
  border-radius: inherit;
}

.num-btn:hover {
  background: var(--bg-hover);
  border-color: var(--accent);
  color: #fff;
  box-shadow: 0 0 12px var(--accent-glow);
  transform: translateY(-1px);
}

.num-btn:active {
  transform: scale(0.93) translateY(0);
}

.num-btn.disabled-num {
  opacity: 0.25;
  pointer-events: none;
}

.erase-btn {
  color: var(--text-muted);
}
.erase-btn:hover {
  color: var(--error);
  border-color: var(--error);
  box-shadow: 0 0 12px rgba(239,68,68,0.2);
}

.undo-bar {
  display: flex;
  gap: 10px;
  justify-content: center;
}

.icon-btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-family: var(--font-ui);
  font-size: 12px;
  font-weight: 500;
  padding: 7px 16px;
  background: var(--bg-card);
  color: var(--text-muted);
  border: 1px solid var(--border-thick);
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all 0.18s ease;
  letter-spacing: 0.04em;
}

.icon-btn:hover:not([disabled]) {
  background: var(--bg-hover);
  color: var(--text);
  border-color: var(--accent);
}

.icon-btn[disabled] {
  opacity: 0.3;
  cursor: not-allowed;
}

.overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 5, 15, 0.85);
  backdrop-filter: blur(8px);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 100;
  padding: 16px;
  animation: fade-in 0.3s ease;
}

.overlay.hidden {
  display: none;
}

@keyframes fade-in {
  from { opacity: 0; }
  to   { opacity: 1; }
}

.overlay-card {
  background: var(--bg-card);
  border: 1px solid var(--border-thick);
  border-radius: 20px;
  padding: 36px 40px;
  text-align: center;
  max-width: 340px;
  width: 100%;
  box-shadow: 0 24px 80px rgba(0,0,0,0.7), 0 0 60px rgba(59,130,246,0.1);
  animation: card-in 0.4s cubic-bezier(0.34,1.56,0.64,1);
}

@keyframes card-in {
  from { transform: scale(0.8) translateY(30px); opacity: 0; }
  to   { transform: scale(1) translateY(0); opacity: 1; }
}

.overlay-icon {
  font-size: 48px;
  color: var(--accent);
  text-shadow: 0 0 30px var(--accent);
  margin-bottom: 16px;
  animation: spin-star 0.6s ease 0.2s both;
}

@keyframes spin-star {
  from { transform: rotate(-180deg) scale(0); opacity: 0; }
  to   { transform: rotate(0) scale(1); opacity: 1; }
}

.overlay-title {
  font-family: var(--font-ui);
  font-size: 26px;
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--text);
  margin-bottom: 6px;
}

.overlay-subtitle {
  font-size: 13px;
  color: var(--text-muted);
  margin-bottom: 24px;
  letter-spacing: 0.04em;
}

.overlay-stats {
  display: flex;
  gap: 20px;
  justify-content: center;
  margin-bottom: 28px;
}

.overlay-buttons {
  display: flex;
  gap: 12px;
  justify-content: center;
}

.o-stat {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 4px;
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 12px 22px;
}

.o-stat span:first-child {
  font-family: var(--font-mono);
  font-size: 22px;
  color: var(--accent);
}

.o-stat span:last-child {
  font-size: 10px;
  letter-spacing: 0.14em;
  color: var(--text-muted);
  text-transform: uppercase;
}

#mistakeCount.warn  { color: var(--warning); }
#mistakeCount.danger { color: var(--error); }

::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: var(--bg); }
::-webkit-scrollbar-thumb { background: var(--border-thick); border-radius: 4px; }

@media (max-width: 480px) {
  body { padding: 16px 10px 32px; }
  :root { --cell-size: min(39px, 10vw); }
  .controls-bar { flex-direction: column; align-items: flex-start; }
  .action-buttons { width: 100%; justify-content: flex-end; }
  .stats-bar { padding: 8px 10px; }
  .stat { padding: 0 10px; }
  .grid-container { padding: 10px; }
  .numpad { max-width: 340px; gap: 5px; }
  .overlay-card { padding: 28px 24px; }
}

@media (max-width: 360px) {
  :root { --cell-size: 36px; }
  .logo-text { font-size: 17px; }
  .timer-display { font-size: 18px; }
}