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

:root {
  --bg: #f0f4f8;
  --surface: #ffffff;
  --primary: #4361ee;
  --text: #1a1a2e;
  --text-light: #6b7280;
  --cell-size: min(52px, calc((100vw - 40px) / 9));
  --border-thin: 1px solid #d1d5db;
  --border-thick: 3px solid #1a1a2e;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  background: var(--bg);
  min-height: 100vh;
  color: var(--text);
}

#app {
  width: 100%;
  max-width: 520px;
  margin: 0 auto;
  min-height: 100vh;
  padding: 20px 16px 32px;
}

/* ── Screens ── */
.screen { display: none; }
.screen.active { display: block; }

#win-screen {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.55);
  align-items: center;
  justify-content: center;
  z-index: 100;
}
#win-screen.show { display: flex; }

/* ── Mode Select ── */
.logo {
  text-align: center;
  padding-top: 24px;
  margin-bottom: 8px;
}
.logo-icon { font-size: 56px; line-height: 1; }
.logo h1 {
  font-size: 38px;
  font-weight: 800;
  color: var(--primary);
  margin-top: 4px;
}
.subtitle {
  text-align: center;
  color: var(--text-light);
  font-size: 15px;
  margin-bottom: 28px;
}

.mode-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 14px;
}

.mode-card {
  background: var(--surface);
  border: none;
  border-radius: 18px;
  padding: 22px 14px;
  cursor: pointer;
  text-align: center;
  box-shadow: 0 2px 10px rgba(0,0,0,0.08);
  transition: transform 0.15s, box-shadow 0.15s;
  -webkit-tap-highlight-color: transparent;
}
.mode-card:hover  { transform: translateY(-3px); box-shadow: 0 6px 18px rgba(0,0,0,0.13); }
.mode-card:active { transform: scale(0.97); }

.beginner-card { border-top: 5px solid #22c55e; }
.easy-card     { border-top: 5px solid #3b82f6; }
.medium-card   { border-top: 5px solid #f59e0b; }
.hard-card     { border-top: 5px solid #ef4444; }

.mode-emoji   { font-size: 36px; margin-bottom: 8px; }
.mode-name    { font-size: 19px; font-weight: 700; margin-bottom: 4px; }
.beginner-card .mode-name { color: #22c55e; }
.easy-card .mode-name     { color: #3b82f6; }
.medium-card .mode-name   { color: #f59e0b; }
.hard-card .mode-name     { color: #ef4444; }
.mode-details { font-size: 12px; color: var(--text-light); }
.mode-age     { font-size: 11px; color: var(--text-light); margin-top: 2px; }

/* ── Top Bar ── */
.top-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 10px;
}

.icon-btn {
  background: var(--surface);
  border: none;
  border-radius: 12px;
  width: 42px; height: 42px;
  display: flex; align-items: center; justify-content: center;
  cursor: pointer;
  color: var(--text);
  box-shadow: 0 1px 6px rgba(0,0,0,0.1);
  transition: background 0.15s;
  -webkit-tap-highlight-color: transparent;
}
.icon-btn svg { width: 18px; height: 18px; }
.icon-btn:hover { background: #e5e7eb; }

.game-stats { display: flex; gap: 24px; }
.stat-box   { text-align: center; }
.stat-val   { font-size: 22px; font-weight: 700; }
.stat-lbl   { font-size: 10px; color: var(--text-light); text-transform: uppercase; letter-spacing: .06em; }

.mode-badge {
  text-align: center;
  font-size: 12px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: .1em;
  color: var(--text-light);
  margin-bottom: 12px;
}

/* ── Board ── */
#board-wrap {
  display: flex;
  justify-content: center;
  margin-bottom: 18px;
}

#board {
  display: grid;
  background: #1a1a2e;
  border: 3px solid #1a1a2e;
  border-radius: 8px;
  overflow: hidden;
  gap: 1px;
  /* grid-template-columns set by JS */
}

.cell {
  background: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  font-size: calc(var(--cell-size) * 0.52);
  font-weight: 600;
  border: none;
  outline: none;
  position: relative;
  user-select: none;
  -webkit-tap-highlight-color: transparent;
  transition: background 0.08s;
  width: var(--cell-size);
  height: var(--cell-size);
}

/* Thick box-border separators for 9×9 */
.board-9x9 .cell.br { border-right: var(--border-thick) !important; }
.board-9x9 .cell.bb { border-bottom: var(--border-thick) !important; }
.board-9x9 .cell.br { border-right: 3px solid #1a1a2e; }
.board-9x9 .cell.bb { border-bottom: 3px solid #1a1a2e; }

/* Right / bottom hairlines between cells */
.cell.thin-r { border-right: var(--border-thin); }
.cell.thin-b { border-bottom: var(--border-thin); }

/* Number states */
.cell.given        { color: #1a1a2e; font-weight: 800; }
.cell.user-correct { color: #3b82f6; }
.cell.user-wrong   { color: #ef4444; }

/* Highlights */
.cell.selected        { background: #bfdbfe !important; }
.cell.same-num        { background: #93c5fd !important; }
.cell.related         { background: #eff6ff; }

/* Beginner color-coded numbers */
.board-3x3 .cell { font-size: calc(var(--cell-size) * 0.6); }
.board-3x3 .cell[data-num="1"] { color: #ef4444; }
.board-3x3 .cell[data-num="2"] { color: #3b82f6; }
.board-3x3 .cell[data-num="3"] { color: #22c55e; }

/* Notes grid inside cell */
.notes-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  width: 100%;
  height: 100%;
  padding: 1px;
}
.note-num {
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: calc(var(--cell-size) * 0.22);
  font-weight: 500;
  color: #6b7280;
  line-height: 1;
}

/* ── Controls ── */
#controls { padding: 0 4px; }

.action-row {
  display: flex;
  gap: 8px;
  justify-content: center;
  margin-bottom: 14px;
}
.action-btn {
  flex: 1;
  max-width: 110px;
  background: var(--surface);
  border: none;
  border-radius: 14px;
  padding: 10px 8px 8px;
  cursor: pointer;
  font-size: 12px;
  font-weight: 600;
  color: var(--text);
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 4px;
  box-shadow: 0 1px 6px rgba(0,0,0,0.08);
  transition: background 0.15s, transform 0.1s;
  -webkit-tap-highlight-color: transparent;
}
.action-btn:hover  { background: #f3f4f6; }
.action-btn:active { transform: scale(0.96); }
.action-btn.active { background: var(--primary); color: #fff; }
.action-btn.active svg { stroke: #fff; }

#numpad {
  display: grid;
  gap: 8px;
}
.numpad-9 { grid-template-columns: repeat(9, 1fr); }
.numpad-3 { grid-template-columns: repeat(3, 1fr); max-width: 220px; margin: 0 auto; }

.num-btn {
  background: var(--surface);
  border: none;
  border-radius: 12px;
  aspect-ratio: 1;
  font-size: clamp(16px, 5vw, 22px);
  font-weight: 700;
  cursor: pointer;
  color: var(--text);
  box-shadow: 0 1px 6px rgba(0,0,0,0.08);
  transition: background 0.12s, transform 0.1s;
  -webkit-tap-highlight-color: transparent;
}
.num-btn:hover  { background: #dbeafe; color: var(--primary); }
.num-btn:active { transform: scale(0.93); }
.num-btn.used   { opacity: 0.25; pointer-events: none; }

/* ── Win Screen ── */
.win-content {
  background: #fff;
  border-radius: 24px;
  padding: 40px 28px;
  text-align: center;
  width: 90%;
  max-width: 360px;
  box-shadow: 0 24px 64px rgba(0,0,0,0.25);
  animation: pop-in 0.35s cubic-bezier(0.34, 1.56, 0.64, 1);
}
@keyframes pop-in {
  from { transform: scale(0.7); opacity: 0; }
  to   { transform: scale(1);   opacity: 1; }
}
.win-emoji  { font-size: 68px; margin-bottom: 10px; }
.win-content h2 { font-size: 28px; font-weight: 800; margin-bottom: 20px; }

.win-stats-row { display: flex; gap: 32px; justify-content: center; margin-bottom: 28px; }
.win-stat-val  { font-size: 26px; font-weight: 700; color: var(--primary); }
.win-stat-lbl  { font-size: 11px; color: var(--text-light); text-transform: uppercase; letter-spacing: .06em; }

.primary-btn {
  display: block;
  width: 100%;
  background: var(--primary);
  color: #fff;
  border: none;
  border-radius: 14px;
  padding: 15px;
  font-size: 16px;
  font-weight: 700;
  cursor: pointer;
  margin-bottom: 10px;
  transition: opacity 0.15s;
}
.primary-btn:hover { opacity: 0.9; }
.secondary-btn {
  display: block;
  width: 100%;
  background: transparent;
  color: var(--text-light);
  border: none;
  padding: 10px;
  font-size: 14px;
  cursor: pointer;
}

/* ── Animations ── */
@keyframes pop   { 0%,100% { transform: scale(1); } 50% { transform: scale(1.2); } }
@keyframes shake { 0%,100% { transform: translateX(0); } 25% { transform: translateX(-5px); } 75% { transform: translateX(5px); } }
.anim-pop   { animation: pop   0.22s ease; }
.anim-shake { animation: shake 0.35s ease; }

/* ── Confetti canvas ── */
#confetti-canvas {
  position: fixed; inset: 0;
  pointer-events: none;
  z-index: 99;
  width: 100%; height: 100%;
}