css实现自适应正方形

1、vm单位

<div class="square-shape"></div>
.square-shape {
  width: 50%;
  height: 50vw;
  border: 1px solid #f00;
}

2、padding-top实现

<div class="square-shape"></div>
.square-shape {
  width: 50%;
  height: 0; 
  padding-top: 50%;
  border: 1px solid #f00;
}

3、padding-bottom实现

<div class="square-shape"></div>
.square-shape {
  width: 50%;
  height: 0;
  padding-bottom: 50%;
  border: 1px solid #f00;
}

4、伪元素的margin-top

<div class="square-shape"></div>
.square-shape {
  width: 100%;
  overflow: hidden;
  border: 1px solid #f00;
}
.square-shape:after {
  content: '';
  display: block;
  margin-top: 100%;
}

5、伪元素的padding-top

<div class="square-shape"></div>
.square-shape {
  width: 30%;
  max-width: 200px;  
  border: 1px solid #f00;
}
.square-shape:after {
  content: '';
  display: block;
  padding-top: 100%;
}

6、子元素margin-top

<div class="square-shape">
  <div class="content"></div>
</div>
.square-shape{
  overflow: hidden;
  width: 50%;
  background-color: black;
}
.content{
  margin-top: 100%;
}

7、伪元素的padding-bottom，内嵌absolute元素

<div class="square-shape">
    <div class="content"></div>
</div>
.square-shape {
  width: 50%;
  border: 1px solid #f00;
}
.square-shape:after {
  content: '';
  display: block;
  padding-bottom: 100%;
}
.content {
  position: absolute;
  width: 100%;
  height: 100%;
}