:root {
  --bg-primary: #0D1117;
  --bg-secondary: #161B22;
  --bg-tertiary: #21262D;
  --text-primary: #F0F6FC;
  --text-secondary: #8B949E;
  --text-muted: #484F58;
  --accent: #3B82F6;
  --border: #30363D;
  --btn-bg: #21262D;
  --btn-active: #30363D;
  --overlay-bg: rgba(0, 0, 0, 0.85);
  --board-bg: #0A0E14;
}

@media (prefers-color-scheme: light) {
  :root {
    --bg-primary: #FFFFFF;
    --bg-secondary: #F6F8FA;
    --bg-tertiary: #E9ECF0;
    --text-primary: #1B1E28;
    --text-secondary: #57606A;
    --text-muted: #8C959F;
    --accent: #3182F6;
    --border: #D0D7DE;
    --btn-bg: #E9ECF0;
    --btn-active: #D0D7DE;
    --overlay-bg: rgba(255, 255, 255, 0.9);
    --board-bg: #F0F2F5;
  }
}

*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
  -webkit-tap-highlight-color: transparent;
}

html, body {
  height: 100%;
  width: 100%;
  overscroll-behavior: none;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Pretendard', 'Segoe UI', Roboto, sans-serif;
  background-color: var(--bg-primary);
  color: var(--text-primary);
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100dvh;
  overflow: hidden;
  position: relative;
}

/* ── App Shell ── */
#app {
  width: 100%;
  max-width: 480px;
  height: 100dvh;
  display: flex;
  flex-direction: column;
  position: relative;
  overflow: hidden;
}

/* ── Overlay Screens ── */
.screen {
  position: absolute;
  inset: 0;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  gap: 20px;
  background: var(--overlay-bg);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  z-index: 10;
  padding: 32px 24px;
  transition: opacity 0.3s ease, transform 0.3s ease;
}

.screen.hidden {
  opacity: 0;
  pointer-events: none;
  transform: scale(0.97);
}

/* ── Start Screen ── */
#start-screen {
  background: var(--bg-primary);
}

.title-block {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
  margin-bottom: 8px;
}

.game-title {
  font-size: 72px;
  font-weight: 900;
  letter-spacing: -2px;
  line-height: 1;
  background: linear-gradient(135deg, var(--accent) 0%, #60A5FA 40%, #A78BFA 80%, #F472B6 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  user-select: none;
}

.game-subtitle {
  font-size: 15px;
  color: var(--text-secondary);
  letter-spacing: 0.5px;
}

.high-score-display {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 4px;
  padding: 14px 32px;
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 12px;
}

.hs-label {
  font-size: 11px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 1.2px;
  color: var(--text-muted);
}

.hs-value {
  font-size: 36px;
  font-weight: 800;
  color: var(--text-primary);
  line-height: 1;
}

.btn-primary {
  width: 100%;
  max-width: 280px;
  padding: 16px 24px;
  border: none;
  border-radius: 14px;
  background: var(--accent);
  color: #fff;
  font-family: inherit;
  font-size: 17px;
  font-weight: 700;
  cursor: pointer;
  transition: transform 0.12s ease, opacity 0.12s ease, box-shadow 0.12s ease;
  box-shadow: 0 4px 24px rgba(59, 130, 246, 0.35);
  letter-spacing: 0.3px;
}

.btn-primary:hover {
  transform: translateY(-1px);
  box-shadow: 0 6px 28px rgba(59, 130, 246, 0.45);
}

.btn-primary:active {
  transform: translateY(0) scale(0.98);
  opacity: 0.9;
}

.btn-secondary {
  width: 100%;
  max-width: 280px;
  padding: 13px 24px;
  border: 1px solid var(--border);
  border-radius: 14px;
  background: var(--btn-bg);
  color: var(--text-secondary);
  font-family: inherit;
  font-size: 15px;
  font-weight: 600;
  cursor: pointer;
  transition: transform 0.12s ease, background 0.12s ease;
}

.btn-secondary:hover {
  background: var(--btn-active);
  color: var(--text-primary);
}

.btn-secondary:active {
  transform: scale(0.98);
}

.rules-text {
  font-size: 13px;
  color: var(--text-muted);
  text-align: center;
  line-height: 1.7;
  max-width: 280px;
}

/* ── Game Screen ── */
#game-screen {
  background: var(--bg-primary);
  justify-content: flex-start;
  padding: 0;
}

.hud {
  width: 100%;
  padding: 16px 20px 12px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  flex-shrink: 0;
  background: var(--bg-primary);
  border-bottom: 1px solid var(--border);
}

.hud-stat {
  display: flex;
  flex-direction: column;
  align-items: center;
  min-width: 56px;
}

.hud-label {
  font-size: 10px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 1px;
  color: var(--text-muted);
  margin-bottom: 2px;
}

.hud-value {
  font-size: 22px;
  font-weight: 800;
  color: var(--text-primary);
  line-height: 1;
}

.hud-value.timer-warning {
  color: #F87171;
  animation: pulse-warning 0.5s ease infinite alternate;
}

@keyframes pulse-warning {
  from { transform: scale(1); }
  to   { transform: scale(1.08); }
}

.lives-display {
  display: flex;
  gap: 5px;
  align-items: center;
}

.heart {
  font-size: 18px;
  transition: transform 0.2s ease, opacity 0.3s ease;
}

.heart.lost {
  opacity: 0.2;
  transform: scale(0.8);
}

/* ── Timer Bar ── */
.timer-bar-wrap {
  width: 100%;
  height: 4px;
  background: var(--bg-tertiary);
  flex-shrink: 0;
  overflow: hidden;
}

.timer-bar {
  height: 100%;
  background: var(--accent);
  width: 100%;
  transform-origin: left center;
  transition: background 0.3s ease;
  will-change: transform;
}

.timer-bar.danger {
  background: #F87171;
}

/* ── Board Container ── */
.board-wrap {
  flex: 1;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  padding: 12px;
  background: var(--bg-primary);
}

.level-badge {
  font-size: 12px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 1.5px;
  color: var(--text-muted);
  margin-bottom: 16px;
}

/* ── Grid Board ── */
#board {
  display: grid;
  gap: 8px;
  background: var(--board-bg);
  padding: 10px;
  border-radius: 16px;
  border: 1px solid var(--border);
  width: 100%;
  max-width: 440px;
  aspect-ratio: 1;
  box-shadow: 0 8px 32px rgba(0, 0, 0, 0.3);
}

.tile {
  border-radius: 10px;
  cursor: pointer;
  transition: transform 0.1s ease;
  border: 2px solid transparent;
  position: relative;
  overflow: hidden;
  will-change: transform;
  min-width: 48px;
  min-height: 48px;
}

.tile::after {
  content: '';
  position: absolute;
  inset: 0;
  background: rgba(255, 255, 255, 0);
  transition: background 0.15s ease;
  border-radius: inherit;
}

.tile:hover::after {
  background: rgba(255, 255, 255, 0.08);
}

.tile:active {
  transform: scale(0.93);
}

.tile.wrong {
  animation: shake 0.35s ease;
  border-color: #F87171 !important;
}

.tile.reveal {
  animation: pulse-reveal 0.6s ease forwards;
  border-color: rgba(255, 255, 255, 0.6) !important;
}

@keyframes shake {
  0%   { transform: translateX(0); }
  20%  { transform: translateX(-6px); }
  40%  { transform: translateX(6px); }
  60%  { transform: translateX(-4px); }
  80%  { transform: translateX(4px); }
  100% { transform: translateX(0); }
}

@keyframes pulse-reveal {
  0%   { transform: scale(1);    box-shadow: 0 0 0 0 rgba(255, 255, 255, 0.6); }
  40%  { transform: scale(1.07); box-shadow: 0 0 0 8px rgba(255, 255, 255, 0); }
  70%  { transform: scale(0.97); }
  100% { transform: scale(1); }
}

/* ── Pause / Game Over Overlays ── */
#pause-screen, #gameover-screen {
  z-index: 20;
}

.overlay-title {
  font-size: 40px;
  font-weight: 900;
  color: var(--text-primary);
  letter-spacing: -1px;
}

.overlay-subtitle {
  font-size: 15px;
  color: var(--text-secondary);
  text-align: center;
}

.score-block {
  display: flex;
  gap: 16px;
}

.score-item {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 4px;
  padding: 16px 24px;
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 12px;
  min-width: 110px;
}

.score-item .label {
  font-size: 11px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 1px;
  color: var(--text-muted);
}

.score-item .value {
  font-size: 38px;
  font-weight: 800;
  color: var(--text-primary);
  line-height: 1;
}

.score-item.highlight .value {
  color: var(--accent);
}

.new-record-badge {
  font-size: 12px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 1.2px;
  color: #FBBF24;
  background: rgba(251, 191, 36, 0.12);
  border: 1px solid rgba(251, 191, 36, 0.3);
  border-radius: 20px;
  padding: 4px 12px;
  display: none;
}

.new-record-badge.visible {
  display: block;
  animation: badge-pop 0.4s cubic-bezier(0.34, 1.56, 0.64, 1);
}

@keyframes badge-pop {
  from { transform: scale(0.5); opacity: 0; }
  to   { transform: scale(1);   opacity: 1; }
}

/* ── Pause button ── */
.btn-icon {
  background: var(--btn-bg);
  border: 1px solid var(--border);
  border-radius: 10px;
  width: 38px;
  height: 38px;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  color: var(--text-secondary);
  font-size: 16px;
  transition: background 0.12s, color 0.12s;
  flex-shrink: 0;
}

.btn-icon:hover {
  background: var(--btn-active);
  color: var(--text-primary);
}

/* ── Feedback Flash ── */
#feedback-flash {
  position: fixed;
  inset: 0;
  pointer-events: none;
  z-index: 30;
  opacity: 0;
  transition: opacity 0.15s ease;
}

#feedback-flash.wrong-flash {
  background: rgba(248, 113, 113, 0.15);
  opacity: 1;
  animation: flash-out 0.4s ease forwards 0.05s;
}

@keyframes flash-out {
  from { opacity: 1; }
  to   { opacity: 0; }
}

/* ── Combo badge ── */
#combo-display {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%) scale(0);
  font-size: 28px;
  font-weight: 900;
  color: var(--accent);
  text-shadow: 0 2px 12px rgba(59, 130, 246, 0.5);
  pointer-events: none;
  z-index: 5;
  opacity: 0;
  white-space: nowrap;
}

#combo-display.show {
  animation: combo-pop 0.7s cubic-bezier(0.34, 1.56, 0.64, 1) forwards;
}

@keyframes combo-pop {
  0%   { transform: translate(-50%, -50%) scale(0); opacity: 0; }
  40%  { transform: translate(-50%, -60%) scale(1.1); opacity: 1; }
  100% { transform: translate(-50%, -80%) scale(0.8); opacity: 0; }
}

/* ── Responsive tweaks ── */
@media (max-height: 700px) {
  .hud {
    padding: 10px 16px 8px;
  }

  .board-wrap {
    padding: 12px 16px;
  }

  .level-badge {
    margin-bottom: 10px;
  }

  #board {
    gap: 5px;
    padding: 6px;
  }

  .game-title {
    font-size: 56px;
  }
}

@media (max-height: 560px) {
  .hud-value {
    font-size: 18px;
  }

  .heart {
    font-size: 14px;
  }

  .level-badge {
    display: none;
  }
}

/* ── Accessibility ── */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
}