:root {
  /* theme tokens */
  --background: #0e131c;
  --foreground: #e8edf5;
  --card: #1a2230;
  --card-foreground: #e8edf5;
  --muted: #232d3f;
  --muted-foreground: #97a2b3;
  --primary: #4f9cf0;
  --primary-foreground: #0b1220;
  --secondary: #3a465c;
  --secondary-foreground: #e8edf5;
  --accent: #f0a35e;
  --accent-foreground: #141a24;
  --destructive: #e05c5c;
  --destructive-foreground: #1c0d0d;
  --border: #2c3648;

  /* spacing + radius scale */
  --sp-xs: 4px; --sp-sm: 8px; --sp-md: 16px; --sp-lg: 24px; --sp-xl: 32px;
  --radius-sm: 8px; --radius-md: 10px; --radius-lg: 16px; --radius-full: 999px;
  --font: system-ui, -apple-system, 'Segoe UI', sans-serif;
}

* { box-sizing: border-box; margin: 0; }

body {
  background: var(--background);
  color: var(--foreground);
  font-family: var(--font);
  line-height: 1.55;
  padding: var(--sp-md);
  display: flex;
  justify-content: center;
}

.screen { width: 100%; max-width: 860px; }
.hidden { display: none !important; }

.visually-hidden {
  position: absolute; width: 1px; height: 1px; overflow: hidden;
  clip: rect(0 0 0 0); white-space: nowrap; border: 0; padding: 0;
}

/* ---------- buttons ---------- */
.btn {
  font: inherit;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--sp-sm);
  border: 1px solid transparent;
  border-radius: var(--radius-md);
  min-height: 44px;
  cursor: pointer;
  color: var(--foreground);
  background: var(--card);
  transition: filter 0.15s ease-out, border-color 0.15s ease-out;
}
.btn:hover:not(:disabled) { filter: brightness(1.12); }
.btn:disabled { opacity: 0.45; cursor: not-allowed; }
.btn:focus-visible { outline: 2px solid var(--primary); outline-offset: 2px; }

.btn-primary { background: var(--primary); color: var(--primary-foreground); }

/* Start Wave button — green to signal "go" */
#btn-start-wave { background: #2e9e4f; color: #fff; }
#btn-start-wave:hover { background: #278743; }

#btn-play { background: #2e9e4f; color: #fff; }
#btn-play:hover:not(:disabled) { background: #278743; filter: none; }
.btn-secondary { background: var(--secondary); color: var(--secondary-foreground); }
.btn-accent { background: var(--accent); color: var(--accent-foreground); }
.btn-danger { background: var(--destructive); color: var(--destructive-foreground); }
.btn-card { background: var(--card); color: var(--foreground); border-color: var(--border); }
.btn-muted { background: var(--muted); color: var(--muted-foreground); border-color: var(--border); }

.btn-xl { font-size: 20px; font-weight: 600; padding: var(--sp-md) var(--sp-lg); width: 100%; }
.btn-lg { font-size: 17px; font-weight: 500; padding: var(--sp-md); width: 100%; }
.btn-md { font-size: 15px; font-weight: 500; padding: var(--sp-sm) var(--sp-md); }
.btn-sm { font-size: 13px; font-weight: 600; padding: var(--sp-sm) var(--sp-md); min-height: 40px; }
.btn-pill { border-radius: var(--radius-full); min-width: 44px; }
.ico { display: inline-block; line-height: 1; font-size: 1.05em; }
.ico-danger { color: var(--destructive); }
.ico-primary { color: var(--primary); }

/* ---------- main menu ---------- */
#menu { display: flex; flex-direction: column; align-items: stretch; gap: var(--sp-lg); max-width: 420px; margin: var(--sp-xl) auto 0; }
.menu-title {
  font-size: 32px; font-weight: 700; text-align: center;
  color: var(--primary); letter-spacing: 1px; line-height: 1.2;
}
.menu-sub { font-size: 17px; text-align: center; color: var(--muted-foreground); }
.btn-group { display: flex; flex-direction: column; gap: var(--sp-md); }
#btn-mute-menu { align-self: center; padding: var(--sp-sm) var(--sp-lg); color: var(--muted-foreground); }

/* ---------- level select ---------- */
.levels-header {
  display: flex; align-items: center; gap: var(--sp-md);
  height: 60px; margin-bottom: var(--sp-lg);
}
.levels-title {
  flex: 1; text-align: center; font-size: 26px; font-weight: 700;
  color: var(--primary); letter-spacing: 2px;
  /* visually center despite back button width */
  margin-right: 52px;
}
.level-grid { display: flex; flex-direction: column; gap: var(--sp-lg); max-width: 640px; margin: 0 auto; }

.level-card {
  display: flex; align-items: center; gap: var(--sp-lg);
  padding: var(--sp-lg);
  background: var(--card); color: var(--card-foreground);
  border: 1px solid var(--border); border-radius: var(--radius-lg);
  text-align: left; font: inherit; cursor: pointer; width: 100%;
  transition: border-color 0.15s ease-out;
}
.level-card:hover:not(:disabled) { border-color: var(--primary); }
.level-card:focus-visible { outline: 2px solid var(--primary); outline-offset: 2px; }
.level-card.locked { cursor: not-allowed; }
.level-num {
  flex: 0 0 auto;
  display: flex; align-items: center; justify-content: center;
  width: 52px; height: 52px; border-radius: var(--radius-full);
  background: var(--primary); color: var(--primary-foreground);
  font-size: 24px; font-weight: 700;
}
.level-card.locked .level-num { background: var(--muted); color: var(--muted-foreground); font-size: 20px; }
.level-info { flex: 1; display: flex; flex-direction: column; gap: var(--sp-xs); min-width: 0; }
.level-name { font-size: 20px; font-weight: 600; }
.level-desc { font-size: 13px; color: var(--muted-foreground); }
.level-best { font-size: 13px; font-weight: 500; color: var(--accent); }
.level-play {
  flex: 0 0 auto; border: 0; border-radius: var(--radius-md);
  background: var(--primary); color: var(--primary-foreground);
  font: inherit; font-size: 13px; font-weight: 700; letter-spacing: 1px;
  padding: var(--sp-sm) var(--sp-md); cursor: pointer; min-height: 44px;
}
.level-play:hover { filter: brightness(1.12); }
.level-play:focus-visible { outline: 2px solid var(--foreground); outline-offset: 2px; }
.locked-badge {
  flex: 0 0 auto; border-radius: var(--radius-full);
  background: var(--destructive); color: var(--destructive-foreground);
  font-size: 11px; font-weight: 700; letter-spacing: 1px;
  padding: var(--sp-xs) var(--sp-sm);
}

/* ---------- game play ---------- */
#game { display: flex; flex-direction: column; gap: var(--sp-md); }
.hud-card {
  display: flex; flex-wrap: wrap; align-items: center; gap: var(--sp-lg) var(--sp-xl);
  padding: var(--sp-md) var(--sp-lg);
  background: var(--card); border: 1px solid var(--border); border-radius: var(--radius-lg);
}
.hud-item { display: flex; align-items: center; gap: var(--sp-sm); }
.hud-coins {
  display: flex; align-items: center; gap: var(--sp-sm);
  background: var(--accent); color: var(--accent-foreground);
  padding: var(--sp-sm) var(--sp-md); border-radius: var(--radius-md);
  font-size: 20px; font-weight: 700;
}
.hud-wave { font-size: 17px; font-weight: 700; letter-spacing: 0.5px; }
.hud-rem { font-size: 13px; font-weight: 500; }
.hud-num { font-size: 13px; font-weight: 700; min-width: 64px; text-align: right; }
.bar-track {
  display: inline-block; width: 120px; height: 12px;
  background: var(--muted); border-radius: var(--radius-full); overflow: hidden;
}
.bar-fill {
  display: block; height: 100%; width: 100%;
  background: var(--destructive); border-radius: var(--radius-full);
  transition: width 0.2s ease-out;
}

.game-area {
  display: flex; gap: var(--sp-md); align-items: flex-start; flex-wrap: wrap;
}
#board {
  flex: 1 1 480px; min-width: 300px; max-width: 800px; aspect-ratio: 4 / 3;
  background: #141a24; border: 1px solid var(--border); border-radius: var(--radius-lg);
  touch-action: none; width: 100%; height: auto;
}

.tower-panel {
  flex: 1 1 260px; max-width: 320px;
  display: flex; flex-direction: column; gap: var(--sp-md);
  padding: var(--sp-lg);
  background: var(--card); border: 1px solid var(--border); border-radius: var(--radius-lg);
}
.panel-title {
  font-size: 17px; font-weight: 700; color: var(--primary);
  text-align: center; letter-spacing: 1px;
}
.tower-cards { display: flex; flex-direction: column; gap: var(--sp-sm); }

.tower-btn {
  position: relative;
  display: flex; align-items: center; gap: var(--sp-sm);
  padding: var(--sp-sm) var(--sp-sm) var(--sp-sm) var(--sp-md);
  background: var(--background); border: 1px solid var(--border);
  border-radius: var(--radius-md); font: inherit; color: var(--foreground);
  cursor: pointer; text-align: left; min-height: 44px;
}
.tower-btn:hover:not(:disabled) { border-color: var(--primary); }
.tower-btn.selected { border-color: var(--primary); }
.tower-btn.selected::after {
  content: ''; position: absolute; left: 2px; top: 8px; bottom: 8px;
  width: 4px; border-radius: var(--radius-full); background: var(--primary);
}
.t-ico {
  flex: 0 0 auto; display: flex; align-items: center; justify-content: center;
  width: 34px; height: 34px; border-radius: var(--radius-sm);
  color: var(--primary-foreground); font-weight: 700;
}
.t-info { display: flex; flex-direction: column; gap: 2px; flex: 1; min-width: 0; }
.t-name { font-size: 13px; font-weight: 700; letter-spacing: 0.5px; }
.t-stats { font-size: 11px; color: var(--muted-foreground); }
.t-cost {
  align-self: flex-start; background: var(--accent); color: var(--accent-foreground);
  border-radius: var(--radius-full); padding: 1px var(--sp-sm);
  font-size: 11px; font-weight: 700; margin-top: 2px;
}

.tower-info {
  font-size: 13px; color: var(--muted-foreground);
  background: var(--background); border: 1px solid var(--border);
  border-radius: var(--radius-sm); padding: var(--sp-sm) var(--sp-md); min-height: 60px;
}
.tower-info button {
  font: inherit; font-size: 13px; padding: var(--sp-xs) var(--sp-md);
  min-height: 44px; margin: var(--sp-xs) var(--sp-xs) 0 0;
  background: var(--muted); color: var(--foreground);
  border: 1px solid var(--border); border-radius: var(--radius-sm); cursor: pointer;
}

.ability-box {
  background: var(--background); border: 1px solid var(--primary);
  border-radius: var(--radius-md); padding: var(--sp-md);
  display: flex; flex-direction: column; gap: var(--sp-sm); align-items: center;
}
.ability-title { font-size: 11px; font-weight: 700; color: var(--primary); letter-spacing: 1px; }
.ability-row { display: flex; gap: var(--sp-sm); flex-wrap: wrap; justify-content: center; }
.ability-row .btn:disabled { opacity: 0.45; }

/* ---------- boss HUD ---------- */
/* Warning banner — spans the HUD card row; pulses while the boss queues.
   The pulse is motion-only decoration: disabled under prefers-reduced-motion. */
.boss-warning {
  flex: 1 0 100%;
  text-align: center;
  font-size: 15px;
  font-weight: 700;
  letter-spacing: 2px;
  color: var(--destructive-foreground);
  background: var(--destructive);
  border-radius: var(--radius-md);
  padding: var(--sp-xs) var(--sp-md);
  animation: boss-warning-pulse 0.9s ease-in-out infinite alternate;
}
@keyframes boss-warning-pulse {
  from { opacity: 1; }
  to { opacity: 0.45; }
}
@media (prefers-reduced-motion: reduce) {
  .boss-warning { animation: none; }
}

/* Boss health bar — hidden until a live boss exists; mirrors bar-track/bar-fill. */
.boss-hud {
  flex: 1 0 100%;
  display: flex;
  align-items: center;
  gap: var(--sp-sm);
}
.boss-hud-name {
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 1.5px;
  color: var(--destructive);
}
.boss-bar-track { flex: 1 1 auto; width: auto; height: 14px; }
.boss-bar-fill { background: var(--destructive); }
@media (max-width: 640px) {
  .boss-warning { font-size: 13px; letter-spacing: 1px; }
  .boss-hud-name { font-size: 12px; }
}

/* ---------- toast + overlay ---------- */
#toast {
  position: fixed; left: 50%; bottom: 24px; transform: translateX(-50%);
  background: var(--card); border: 1px solid var(--primary);
  border-radius: var(--radius-md); padding: var(--sp-sm) var(--sp-md);
  font-size: 14px; color: var(--foreground); z-index: 30;
}
#overlay {
  position: fixed; inset: 0; background: rgba(8, 12, 18, 0.85);
  display: flex; align-items: center; justify-content: center; padding: var(--sp-md);
  z-index: 20;
}
#overlay-card {
  background: var(--card); border: 1px solid var(--border); border-radius: var(--radius-lg);
  padding: var(--sp-lg); max-width: 380px; width: 100%; text-align: center;
  display: flex; flex-direction: column; gap: var(--sp-md);
}
#overlay-title { font-size: 24px; font-weight: 700; color: var(--primary); }
#overlay-body { color: var(--foreground); }
#overlay-list { display: flex; flex-direction: column; gap: var(--sp-xs); color: var(--muted-foreground); font-size: 14px; }
#overlay-action:empty { display: none; }
.overlay-actions { display: flex; flex-direction: column; gap: var(--sp-sm); }
#overlay-paused { margin-top: var(--sp-xs); }

/* ---------- responsive ---------- */
@media (max-width: 640px) {
  .game-area { flex-direction: column; }
  .tower-panel { max-width: none; }
  .menu-title { font-size: 24px; }
  .hud-card { gap: var(--sp-sm) var(--sp-md); padding: var(--sp-sm) var(--sp-md); }
  .hud-num { min-width: 52px; font-size: 12px; }
  .bar-track { width: 80px; }
  #board { min-width: 0; }
  .tower-panel { padding: var(--sp-md); }
  .btn-sm { min-height: 44px; padding: var(--sp-sm) var(--sp-md); }
}
@media (prefers-reduced-motion: reduce) {
  * { transition: none !important; }
}