body {
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
  margin: 0;
  flex-direction: column; /* 垂直居中 */
}

/* 添加标题样式 */
#title {
  font-size: 36px;
  font-weight: bold;
  margin-bottom: 220px;
}

#sudoku-container {
  position: relative;
  display: grid;
  grid-template-columns: repeat(9, 50px);
  grid-template-rows: repeat(9, 50px);
  gap: 1px;
  transform: scale(1.25);
  }

.cell {
  margin-top: -50px;
  width: 50px;
  height: 50px;
  border: 1px solid #ccc;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 18px;
  cursor: pointer;
}

.selected {
  background-color: lightblue;
}

#generate-btn {
  position: absolute;
  top: 200px;
  right: 760px;
  transform: translateX(50%);
  padding: 6.25px 12.5px;
  cursor: pointer;
  z-index: 1; /* Set z-index to keep the button above the grid */
  font-size: 18px;
}

#check-btn {
  /* 与出题按钮一样的样式 */
  position: absolute;
  top: 200px;
  right: 645px;
  transform: translateX(50%);
  padding: 6.25px 12.5px;
  cursor: pointer;
  z-index: 1;
  font-size: 18px;
}


#difficulty-nav {
  position: absolute;
  top: 200px;
  left: 610px;
  display: flex;
  gap: 10px;
}

#difficulty-nav a {
  text-decoration: none;
  padding: 5px 10px;
  border: 1px solid #000;
  cursor: pointer;
  color: #000;
}

.alert-container {
  position: fixed;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  background-color: white;
  border: 1px solid #ccc;
  padding: 20px;
  font-size: 18px;
  font-weight: bold;
  color: green;
}


#sudoku-container .cell.user-input {
  color: blue;
}

/* 除了第1、4、7、10列之外的竖线为浅色 */
#sudoku-container .cell:not(.first-col):not(.fourth-col):not(.seventh-col):not(.tenth-col)::before {
  background-color: #ccc !important;
}

/* 除了第1、4、7、10行之外的横线为浅色 */
#sudoku-container .cell:not(.first-row):not(.fourth-row):not(.seventh-row):not(.tenth-row)::before {
  background-color: #ccc !important;
}

/* 第1、4、7、10列为黑色 */
#sudoku-container .first-col::before,
#sudoku-container .fourth-col::before,
#sudoku-container .seventh-col::before,
#sudoku-container .tenth-col::before {
  background-color: black !important;
}

/* 第1、4、7、10行为黑色 */
#sudoku-container .first-row::before,
#sudoku-container .fourth-row::before,
#sudoku-container .seventh-row::before,
#sudoku-container .tenth-row::before {
  background-color: black !important;
}