背景透明

方法

css3的opacity:x，x 的取值从 0 到 1，如opacity: 0.8
css3的rgba(red, green, blue, alpha)，alpha的取值从 0 到 1，如rgba(255,255,255,0.8)
IE专属滤镜 filter:Alpha(opacity=x)，x 的取值从 0 到 100，如filter:Alpha(opacity=80)

示例

<template>
  <div>
    <div class="regisBg">
      <div class="formStyle">

      </div>
    </div>
  </div>
</template>

<style scoped>
  .regisBg{
    /*margin-top: 30px;*/
    /*margin-bottom: 30px;*/
    height: 500px;
    background-image: url("../../../static/image/registered_back_img.png");
    background-repeat: no-repeat;
    background-size: 100% 100%;
  }
  .formStyle{
    margin-top: 50px;
    margin-right:150px;
    float: right;
    height: 400px;
    width: 500px;
    background-color: #017CCA;

    filter:alpha(opacity=50);
    -moz-opacity:0.5;
    -khtml-opacity: 0.5;
    opacity: 0.5;
  }
</style>

子元素不受影响

 background-color:rgba(1,124,202,0.5) ;