考察知识：
flex布局 + 水平垂直居中的实现
初始效果
代码关键：给父盒子添加以下属性
flex-wrap: wrap; /* 允许换行 */justify-content: space-around; /* 主轴对齐方式 */align-content: space-around; /* 多行在侧轴上的对齐方式 */
<!DOCTYPE html>
<html lang="zn-ch"><head><meta charset="UTF-8" /><meta http-equiv="X-UA-Compatible" content="IE=edge" /><meta name="viewport" content="width=device-width, initial-scale=1.0" /><title>flex九宫格</title></head><body><div class="box"><div class="item">1</div><div class="item">2</div><div class="item">3</div><div class="item">4</div><div class="item">5</div><div class="item">6</div><div class="item">7</div><div class="item">8</div><div class="item">9</div></div></body><script></script><style lang="scss">.box {width: 400px;height: 400px;border: 1px solid red;display: flex; /* */flex-wrap: wrap; /* 允许换行 */justify-content: space-around; /* 主轴对齐方式 */align-content: space-around; /* 多行在侧轴上的对齐方式 */.item {width: 100px;height: 100px;background-color: pink;border: 1px solid red;}}</style>
</html>优化：每个小盒子的内容水平垂直居中
<body><div class="box"><div class="item"><div class="pink"></div>item-name</div><div class="item"><div class="pink"></div>item-name</div><div class="item"><div class="pink"></div>item-name</div><div class="item"><div class="pink"></div>item-name</div><div class="item"><div class="pink"></div>item-name</div><div class="item"><div class="pink"></div>item-name</div><div class="item"><div class="pink"></div>item-name</div><div class="item"><div class="pink"></div>item-name</div><div class="item"><div class="pink"></div>item-name</div></div></body><script></script><style lang="scss">.box {width: 400px;height: 400px;border: 1px solid red;display: flex; /* */flex-wrap: wrap; /* 允许换行 */justify-content: space-around; /* 主轴对齐方式 */align-content: space-around; /* 多行在侧轴上的对齐方式 */.item {width: 100px;height: 100px;background-color: skyblue;border: 1px solid red;display: flex;flex-wrap: wrap;justify-content: center;align-content: center;.pink {width: 50px;height: 50px;border-radius: 50%;background-color: pink;}}}</style>
)
