垂直水平居中的五种写法

方法一、 用disition方法 通过justify

.a {
  width: 100px;
  height: 100px;
  background: red;
  display: flex;
  justify-content: center;
  align-items: center;
}
.b {
  width: 50px;
  height: 50px;
  background: pink;
}

方法二、

.a {
  width: 100px;
  height: 100px;
  background: red;
  position: relative;
}
.b {
  width: 50px;
  height: 50px;
  background: pink;
  position: absolute;
  top: 50%;
  left: 50%;
  margin-top: -25;
  margin-left: -25px;
}

方法三、

.a {
  width: 100px;
  height: 100px;
  background: red;
  position: relative;
}
.b {
  width: 50px;
  height: 50px;
  background: pink;
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
}

方法四、css3新属性设置垂直居中。margin：auto设置水平居中

.a {
  width: 100px;
  height: 100px;
  background: red;
  display: table-cell;
  vertical-align: middle;
}
.b {
  width: 50px;
  height: 50px;
  background: pink;
  margin: auto;
}

方法五、

.a {
  width: 100px;
  height: 100px;
  background: red;
  position: relative;
}
.b {
  width: 50px;
  height: 50px;
  background: pink;
  position: absolute;
  top: 50%;
  left: 50;
  transform: translate(-50%, -50%);
}