块元素垂直水平居中的方法

1、使用flex

.parent {
    height: 600px;
    border: 1px solid red;
    
    display: flex; 
    justify-content: center;
    align-items: center;
}
.child {
    border: 1px solid green;
       300px;
}

2、使用transform

.parent{
  height: 600px;
  border: 1px solid red;
  position: relative;
}
.child{
  border: 1px solid green;
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%,-50%);
}

3、使用margin-top -一半的高度

.parent{
  height: 600px;
  border: 1px solid red;
  position: relative;
}
.child{
  border: 1px solid green;
   300px;
  height: 100px;
  position: absolute;
  top: 50%;
  left: 50%;
  margin-left: -150px;
  margin-top: -50px;
}

4、使用绝对布局absolute和margin:auto

.parent{
  height: 600px;
  border: 1px solid red;
  position: relative;
}
.child{
  border: 1px solid green;
  position: absolute;
   300px;
  height: 200px;
  margin: auto;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
}