body {
    background-color: #fff;
}
#a {
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  box-sizing: border-box;
  width: 100%;
  height: -webkit-calc(9em + 150px);
  height: calc(3em + 90px);/*边框高度*/
  margin: 0 0 1em;
  padding: 1em;
  border: 1px solid #cccccc;
  border-radius: 0.8em;/*弧度大小*/
  background: #fff;
  resize: none;
  outline: none;
  margin-top:20px;
}
#a[required]:focus {
  border-color: #00bafa;
}
input[type="a"][required]:focus + label[placeholder]:before {
  color: #ffffff;/*上跳后的字体颜色*/
}
#a[required]:focus + label[placeholder]:before,
#a[required]:valid + label[placeholder]:before {
  -webkit-transition-duration: .2s;
  transition-duration: .2s;
  -webkit-transform: translate(0, -1.5em) scale(0.9, 0.9);
  -ms-transform: translate(0, -1.5em) scale(0.9, 0.9);
  transform: translate(0, -2.5em)/*上跳的高度*/ scale(1, 1) ;
}
#a[required]:invalid + label[placeholder][alt]:before {
  content: attr(alt);
}
#a[required] + label[placeholder] {
  display: block;
  pointer-events: none;
  font-family:"微软雅黑";
  font-size:14px;



  margin-top: -webkit-calc(-12.5em - 12.5px);
  margin-top: calc(-12.5em - 12.5px);/*虚拟的字体位置*/
  margin-bottom: -webkit-calc((3em - 1em) + 2px);
  margin-bottom: calc((3em - 1em) + 2px);
}
#a{font-family:"微软雅黑";
  font-size:14px;}
#a[required] + label[placeholder]:before {
  
  display: inline-block;
  margin: 0 -webkit-calc(1em + 2px);
  margin: 0 calc(1em + 2px);

  color: #898989;
 
  -webkit-transition: 0.3s ease-in-out;
  transition: 0.3s ease-in-out;
    background-image: -webkit-linear-gradient;/*省略前面的字*/
  -webkit-background-size: 100% 5px;
  background-size: 100% 5px;
  background-repeat: no-repeat;

}