body {
  font-family: Arial, sans-serif;
  background-color: #f5f5f5;
  margin: 0;
  padding: 20px;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
}

.container {
  background-color: white;
  padding: 30px;
  border-radius: 10px;
  box-shadow: 0 0 20px rgba(0, 0, 0, 0.1);
  max-width: 600px;
  width: 100%;
  text-align: center;
}

h1 {
  color: #333;
  margin-bottom: 20px;
}

.sudoku-container {
  display: flex;
  justify-content: center;
  margin-bottom: 20px;
}

#sudoku-grid {
  border-collapse: collapse;
  border: 3px solid #333;
}

#sudoku-grid td {
  width: 40px;
  height: 40px;
  border: 1px solid #999;
  text-align: center;
  font-size: 20px;
  position: relative;
}

#sudoku-grid input {
  width: 100%;
  height: 100%;
  border: none;
  text-align: center;
  font-size: 20px;
  background-color: transparent;
}

#sudoku-grid input:focus {
  outline: 2px solid #4caf50;
  background-color: #f8fff8;
}

#sudoku-grid tr:nth-child(3n) td {
  border-bottom: 2px solid #333;
}

#sudoku-grid tr td:nth-child(3n) {
  border-right: 2px solid #333;
}

.controls {
  margin-bottom: 20px;
}

button {
  background-color: #4caf50;
  color: white;
  border: none;
  padding: 10px 20px;
  margin: 0 5px;
  border-radius: 5px;
  cursor: pointer;
  font-size: 16px;
  transition: background-color 0.3s;
}

button:hover {
  background-color: #45a049;
}

#message {
  min-height: 24px;
  color: #d32f2f;
  font-weight: bold;
}

.solved {
  color: #4caf50;
  font-weight: bold;
}