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

/* ---- Theme tokens ---- */
:root {
  --bg:           #111;
  --bg-cell:      #1a1a1a;
  --bg-spinner:   rgba(17, 17, 17, 0.6);
  --text:         #eee;
  --text-muted:   #888;
  --text-hover:   #ccc;
  --border:       #444;
  --border-focus: #888;

  /* Responsive scale */
  --cell: clamp(58px, 16vw, 80px);
  --gap:  clamp(6px, 1.6vw, 10px);
}

body.light {
  --bg:           #f5f5f5;
  --bg-cell:      #ffffff;
  --bg-spinner:   rgba(245, 245, 245, 0.7);
  --text:         #1a1a1a;
  --text-muted:   #777;
  --text-hover:   #333;
  --border:       #ccc;
  --border-focus: #555;
}

/* ---- Theme toggle button ---- */
#theme-toggle {
  position: fixed;
  top: 16px;
  right: 16px;
  width: 36px;
  height: 36px;
  border-radius: 50%;
  border: 2px solid var(--border);
  background: transparent;
  color: var(--text-muted);
  font-size: 1.1rem;
  line-height: 1;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: border-color 0.15s, color 0.15s;
  z-index: 100;
}

#theme-toggle:hover {
  border-color: var(--border-focus);
  color: var(--text);
}

/* Icon via pseudo-element so JS only touches the class */
#theme-toggle::before { content: '☀︎'; }
body.light #theme-toggle::before { content: '☾'; }

/* ---- Toast ---- */
#toast {
  position: fixed;
  top: 28px;
  left: 50%;
  transform: translateX(-50%) translateY(-12px);
  background: #c0392b;
  color: #fff;
  padding: clamp(8px, 2vw, 10px) clamp(18px, 5vw, 28px);
  border-radius: 999px;
  font-size: clamp(0.78rem, 2.5vw, 0.88rem);
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.18s ease, transform 0.18s ease;
  z-index: 999;
  white-space: nowrap;
  box-shadow: 0 4px 18px rgba(0,0,0,0.4);
}

#toast.visible {
  opacity: 1;
  transform: translateX(-50%) translateY(0);
}

/* ---- Base ---- */
body {
  background: var(--bg);
  color: var(--text);
  font-family: 'Segoe UI', system-ui, sans-serif;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  padding: 24px 16px;
  transition: background 0.2s, color 0.2s;
}

#app {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: clamp(16px, 3.5vw, 28px);
  width: 100%;
  max-width: 520px;
}

h1 {
  font-size: clamp(2rem, 8vw, 3rem);
  letter-spacing: 0.15em;
  text-transform: uppercase;
}

.subtitle {
  color: var(--text-muted);
  font-size: clamp(0.8rem, 2.8vw, 1rem);
  letter-spacing: 0.05em;
  text-align: center;
}

/* ---- Difficulty picker ---- */
#difficulty-picker {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: clamp(6px, 1.5vw, 12px);
}

.diff-btn {
  padding: clamp(7px, 1.5vw, 10px) clamp(16px, 4vw, 28px);
  border: 2px solid var(--border);
  border-radius: 999px;
  background: transparent;
  color: var(--text-muted);
  font-size: clamp(0.78rem, 2.5vw, 0.95rem);
  font-weight: 600;
  letter-spacing: 0.08em;
  cursor: pointer;
  transition: border-color 0.15s, color 0.15s;
}

.diff-btn:hover {
  border-color: var(--border-focus);
  color: var(--text-hover);
}

.diff-btn.active {
  border-color: var(--text);
  color: var(--text);
}

.diff-btn--daily {
  border-color: #a78bfa;
  color: #a78bfa;
}

.diff-btn--daily:hover,
.diff-btn--daily.active {
  border-color: #c4b5fd;
  color: #c4b5fd;
}

.diff-btn--superhard {
  border-color: #f87171;
  color: #f87171;
}

.diff-btn--superhard:hover,
.diff-btn--superhard.active {
  border-color: #fca5a5;
  color: #fca5a5;
}

/* ---- Grid ---- */
#grid {
  display: flex;
  flex-direction: column;
  gap: var(--gap);
}

.row {
  display: flex;
  gap: var(--gap);
  position: relative;
}

.cell {
  width: var(--cell);
  height: var(--cell);
  border: 2px solid var(--border);
  background: var(--bg-cell);
  color: var(--text);
  font-size: calc(var(--cell) * 0.4);
  font-weight: 700;
  text-align: center;
  text-transform: uppercase;
  outline: none;
  caret-color: transparent;
  letter-spacing: 0;
  transition: border-color 0.15s, background 0.3s;
}

.cell:focus {
  border-color: var(--border-focus);
}

.cell[readonly] {
  cursor: default;
}

/* Endpoint circles — color wins over focus, highlights, shake, and error states */
.cell.endpoint-gold,
.cell.endpoint-gold:focus,
.cell.endpoint-gold.special-1,
.cell.endpoint-gold.special-2,
.cell.endpoint-gold.error,
.row.shake .cell.endpoint-gold {
  border-color: #ffd700;
  border-width: 3px;
  border-radius: 50%;
}

.cell.endpoint-teal,
.cell.endpoint-teal:focus,
.cell.endpoint-teal.special-1,
.cell.endpoint-teal.special-2,
.cell.endpoint-teal.error,
.row.shake .cell.endpoint-teal {
  border-color: #2dd4d4;
  border-width: 3px;
  border-radius: 50%;
}

/* Path cells */
.cell.special-1 {
  background: #b8860b;
  border-color: #ffd700;
  color: #fff;
}

.cell.special-2 {
  background: #0e6b6b;
  border-color: #2dd4d4;
  color: #fff;
}

/* Hard mode blocker */
.cell.blocker {
  border-color: #e05050;
  border-width: 3px;
}

/* Invalid flash */
.cell.error {
  border-color: #e05050;
}

/* Shake animation */
@keyframes shake {
  0%, 100% { transform: translateX(0); }
  20%       { transform: translateX(-8px); }
  40%       { transform: translateX(8px); }
  60%       { transform: translateX(-5px); }
  80%       { transform: translateX(5px); }
}

.row.shake { animation: shake 0.35s ease; }
.row.shake .cell { border-color: #e05050; }

/* ---- Spinner ---- */
#game-area {
  position: relative;
}

#spinner {
  display: none;
  position: absolute;
  inset: 0;
  background: var(--bg-spinner);
  border-radius: 4px;
  align-items: center;
  justify-content: center;
}

#spinner.visible { display: flex; }

#spinner::after {
  content: '';
  width: clamp(32px, 6vw, 44px);
  height: clamp(32px, 6vw, 44px);
  border: 3px solid var(--border);
  border-top-color: var(--text);
  border-radius: 50%;
  animation: spin 0.7s linear infinite;
}

@keyframes spin {
  to { transform: rotate(360deg); }
}

/* ---- Bottom bar ---- */
#bottom-bar {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: clamp(6px, 1.5vw, 12px);
}

#reset-btn, #clear-btn, #share-btn {
  padding: clamp(7px, 1.5vw, 10px) clamp(16px, 4vw, 28px);
  border: 2px solid var(--border);
  border-radius: 999px;
  background: transparent;
  color: var(--text-muted);
  font-size: clamp(0.78rem, 2.5vw, 0.95rem);
  font-weight: 600;
  letter-spacing: 0.08em;
  cursor: pointer;
  transition: border-color 0.15s, color 0.15s;
}

#reset-btn:hover, #clear-btn:hover, #share-btn:hover {
  border-color: var(--border-focus);
  color: var(--text-hover);
}

#message {
  font-size: clamp(0.8rem, 2.5vw, 0.95rem);
  color: var(--text-muted);
  letter-spacing: 0.05em;
  height: 1.2em;
  text-align: center;
}