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

body {
  font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
  background: linear-gradient(135deg, #0f0c29, #302b63, #24243e);
  min-height: 100vh;
  display: flex;
  justify-content: center;
  padding: 20px;
  color: #e0e0e0;
}

.container {
  max-width: 700px;
  width: 100%;
  text-align: center;
}

h1 {
  font-size: 2.2rem;
  margin-bottom: 24px;
  background: linear-gradient(90deg, #f6d365, #fda085);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  text-shadow: none;
}

.controls {
  display: flex;
  flex-direction: column;
  gap: 14px;
  margin-bottom: 24px;
}

.size-selector, .difficulty-selector, .actions {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 10px;
  flex-wrap: wrap;
}

label {
  font-size: 0.95rem;
  color: #aaa;
}

button {
  border: none;
  cursor: pointer;
  border-radius: 8px;
  font-size: 0.9rem;
  transition: all 0.2s;
}

.size-btn, .diff-btn {
  padding: 8px 18px;
  background: rgba(255,255,255,0.08);
  color: #ccc;
  border: 1px solid rgba(255,255,255,0.12);
}

.size-btn:hover, .diff-btn:hover {
  background: rgba(255,255,255,0.15);
}

.size-btn.active {
  background: linear-gradient(135deg, #667eea, #764ba2);
  color: #fff;
  border-color: transparent;
  box-shadow: 0 2px 12px rgba(102,126,234,0.4);
}

.diff-btn.active {
  background: linear-gradient(135deg, #f093fb, #f5576c);
  color: #fff;
  border-color: transparent;
  box-shadow: 0 2px 12px rgba(245,87,108,0.4);
}

.action-btn {
  padding: 10px 28px;
  font-size: 1rem;
  font-weight: 600;
  color: #fff;
}

.action-btn.solve {
  background: linear-gradient(135deg, #11998e, #38ef7d);
  box-shadow: 0 3px 14px rgba(56,239,125,0.3);
}

.action-btn.generate {
  background: linear-gradient(135deg, #667eea, #764ba2);
  box-shadow: 0 3px 14px rgba(102,126,234,0.3);
}

.action-btn.clear {
  background: rgba(255,255,255,0.1);
  border: 1px solid rgba(255,255,255,0.2);
}

.action-btn:hover {
  transform: translateY(-1px);
  filter: brightness(1.1);
}

.action-btn:active {
  transform: translateY(0);
}

/* Board */
.board-wrapper {
  display: flex;
  justify-content: center;
  margin-bottom: 20px;
}

#board {
  display: inline-grid;
  gap: 0;
  user-select: none;
}

.cell {
  width: 56px;
  height: 56px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.4rem;
  font-weight: 700;
  position: relative;
}

/* Clue cells (around the border) */
.cell.clue {
  color: #f6d365;
  font-size: 1.1rem;
  font-weight: 600;
}

.cell.clue input {
  width: 100%;
  height: 100%;
  border: none;
  background: transparent;
  text-align: center;
  font-size: 1.1rem;
  font-weight: 600;
  color: #f6d365;
  outline: none;
  caret-color: #f6d365;
}

.cell.clue input::placeholder {
  color: rgba(246,211,101,0.25);
}

.cell.clue input:focus {
  background: rgba(246,211,101,0.08);
  border-radius: 6px;
}

/* Corner cells (empty) */
.cell.corner {
  /* empty */
}

/* Grid cells */
.cell.grid-cell {
  background: rgba(255,255,255,0.04);
  border: 1px solid rgba(255,255,255,0.1);
}

.cell.grid-cell input {
  width: 100%;
  height: 100%;
  border: none;
  background: transparent;
  text-align: center;
  font-size: 1.5rem;
  font-weight: 700;
  color: #e0e0e0;
  outline: none;
  caret-color: #38ef7d;
}

.cell.grid-cell input::placeholder {
  color: rgba(255,255,255,0.12);
}

.cell.grid-cell input:focus {
  background: rgba(102,126,234,0.12);
}

.cell.grid-cell.solved input {
  color: #38ef7d;
}

.cell.grid-cell.user-filled input {
  color: #82b1ff;
}

.cell.grid-cell.error {
  background: rgba(245,87,108,0.15);
}

.cell.grid-cell.error input {
  color: #f5576c;
}

/* Message */
.message {
  min-height: 28px;
  margin-bottom: 16px;
  font-size: 0.95rem;
  transition: all 0.3s;
}

.message.success {
  color: #38ef7d;
}

.message.error {
  color: #f5576c;
}

.message.info {
  color: #82b1ff;
}

/* Instructions */
.instructions {
  background: rgba(255,255,255,0.04);
  border: 1px solid rgba(255,255,255,0.08);
  border-radius: 12px;
  padding: 18px 24px;
  text-align: left;
  margin-top: 10px;
}

.instructions h3 {
  margin-bottom: 8px;
  color: #aaa;
  font-size: 0.95rem;
}

.instructions p {
  font-size: 0.85rem;
  color: #888;
  margin-bottom: 4px;
  line-height: 1.6;
}

/* Responsive */
@media (max-width: 500px) {
  .cell {
    width: 44px;
    height: 44px;
    font-size: 1.1rem;
  }
  .cell.grid-cell input { font-size: 1.2rem; }
  .cell.clue input { font-size: 0.95rem; }
  h1 { font-size: 1.6rem; }
}