* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: Arial, sans-serif;
  background: #f4f4f4;
  color: #222;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
}

.game-container {
  text-align: center;
  padding: 24px;
}

h1 {
  margin: 0 0 8px;
  font-size: 2rem;
}

.subtitle {
  margin: 0 0 24px;
  color: #666;
}

.sudoku-board {
  display: grid;
  grid-template-columns: repeat(9, 50px);
  grid-template-rows: repeat(9, 50px);
  border: 3px solid #222;
  background: #fff;
  margin: 0 auto 20px;
}

.cell {
  width: 50px;
  height: 50px;
  border: 1px solid #999;
  text-align: center;
  font-size: 1.2rem;
  font-weight: bold;
  outline: none;
}

.cell:focus {
  background: #eaf4ff;
}

.fixed {
  background: #e9e9e9;
  color: #111;
}

.editable {
  background: #fff;
  color: #1a4fb8;
}

.correct {
  background: #e7f6ea;
}

.incorrect {
  background: #fdeaea;
  color: #b42318;
}

.border-right {
  border-right: 3px solid #222 !important;
}

.border-bottom {
  border-bottom: 3px solid #222 !important;
}

.actions {
  margin-bottom: 16px;
}

button {
  padding: 10px 18px;
  font-size: 1rem;
  border: none;
  border-radius: 8px;
  cursor: pointer;
  background: #1a4fb8;
  color: white;
}

button:hover {
  opacity: 0.95;
}

.message {
  min-height: 24px;
  font-weight: bold;
}

@media (max-width: 560px) {
  .sudoku-board {
    grid-template-columns: repeat(9, 38px);
    grid-template-rows: repeat(9, 38px);
  }

  .cell {
    width: 38px;
    height: 38px;
    font-size: 1rem;
  }

  h1 {
    font-size: 1.6rem;
  }
}