body {
  font-family: 'Segoe UI', sans-serif;
  background: #f5f5f5;
  text-align: center;
  margin: 0;
  padding: 20px;
}

h1 {
  color: #333;
}

#timer {
  font-size: 20px;
  margin-bottom: 10px;
  color: #666;
}

#sudoku {
  display: grid;
  grid-template-columns: repeat(9, 40px);
  gap: 2px;
  justify-content: center;
  margin: 20px auto;
}

input {
  width: 38px;
  height: 38px;
  text-align: center;
  font-size: 18px;
  border: 1px solid #bbb;
  background: #fff;
  outline: none;
}

input:disabled {
  background: #ddd;
}

.bold-right { border-right: 2px solid black; }
.bold-bottom { border-bottom: 2px solid black; }

.buttons {
  margin-top: 20px;
}

button {
  margin: 5px;
  padding: 10px 15px;
  font-size: 16px;
  background: #333;
  color: white;
  border: none;
  cursor: pointer;
}

button:hover {
  background: #555;
}