.sudoku-container {
  background: rgba(255, 255, 255, 0.1);
  padding: 2rem;
  border-radius: 15px;
  box-shadow: 0 0 20px rgba(0, 0, 0, 0.3);
}

h1 {
  text-align: center;
  margin-bottom: 2rem;
  color: #00a8ff;
}

#sudoku-board {
  border-collapse: collapse;
  margin: 20px auto;
  background: #ffffff;
  border-radius: 8px;
  border: 2px solid #00a8ff;
}

td {
  width: 50px;
  height: 50px;
  text-align: center;
  border: 1px solid #cccccc;
  color: #000000;
  font-size: 1.2em;
  transition: all 0.3s ease;
  cursor: pointer;
}

td:nth-child(3n) {
  border-right: 2px solid #00a8ff;
}

tr:nth-child(3n) td {
  border-bottom: 2px solid #00a8ff;
}

td:focus {
  background-color: rgba(0, 168, 255, 0.1);
  outline: none;
}

td.initial {
  background-color: #f0f0f0;
  cursor: not-allowed;
}

td.invalid {
  background-color: rgba(255, 0, 0, 0.1);
}

td:nth-child(3n) {
  border-right: 2px solid #00a8ff;
}

tr:nth-child(3n) td {
  border-bottom: 2px solid #00a8ff;
}

td:focus {
  background: rgba(0, 168, 255, 0.2);
  outline: none;
}

.controls {
  display: flex;
  gap: 1rem;
  justify-content: center;
  margin: 20px 0;
}

button {
  padding: 10px 20px;
  border: none;
  border-radius: 5px;
  background: #00a8ff;
  color: white;
  cursor: pointer;
  transition: all 0.3s ease;
}

button:hover {
  background: #0084ff;
  transform: translateY(-2px);
}

#difficulty-selector {
  text-align: center;
  margin: 1rem 0;
}

select {
  padding: 5px 10px;
  border-radius: 5px;
  background: #1f2937;
  color: white;
  border: 1px solid #00a8ff;
}

#timer, #lives-display {
  text-align: center;
  font-size: 1.2em;
  margin-top: 1rem;
  color: #00a8ff;
}

#lives-display {
  font-weight: bold;
}

.initial {
  color: #00a8ff;
}

.invalid {
  color: #ff4444;
}