说说css伪元素::before和::after，你就会明白我们为什么需要它

wxml

1   <view class='weui-loading'>#000</view>
2 
3   <view class='btn'><text class='green'>前面</text>#000</view>

css

/* 
  说说伪元素::before和::after,也许你会更加清晰 
  
*/

.weui-loading {
  position: relative;
  display: block;
  margin-left: auto;
  margin-right: auto;
  padding-left: 14px;
  padding-right: 14px;
  box-sizing: border-box;
  font-size: 18px;
  text-align: center;
  color: #000;
  text-decoration: none;
  line-height: 2.55555556;
  border-radius: 5px;
  -webkit-tap-highlight-color: rgba(0, 0, 0, 0);
  overflow: hidden;
}

/* 为了兼容低版本,使用:before */
.weui-loading:before {
}

.weui-loading::before {
  content: '前面';
  color: #179b16;
}

/* 为了兼容低版本,使用:after */
.weui-loading:after {
}

.weui-loading::after {
  /* 如果content,也就是内容不连接的话,那么content就不会起作用 */
  content: '后面';
  color: #ec350c;
  border: 1px solid #ddd;
  width: 200%;
  height: 200%;
  position: absolute;
  top: 0;
  left: 0;
  -webkit-transform: scale(0.5);
  transform: scale(0.5);
  -webkit-transform-origin: 0 0;
  transform-origin: 0 0;
  box-sizing: border-box;
  border-radius: 10px;
}

.btn {
  color: #000;
  width: 180rpx;
  text-align: center;
  padding: 2%;
  border-radius: 5px;
  border: 1px solid #ddd;
  margin-top: 1%;
}

.btn .green{
  color: #179b16;
}