文章主要介绍了纯css实现输入框placeholder动效及输入校验，文中通过示例代码介绍的非常详细，对大家的学习或者工作具有一定的参考学习价值

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背景

话不多说，我们能否用纯css实现以下效果:

答案是肯定的。

借助css:placeholder-shown :valid :invalid伪类及html5 input pattern 属性就可以实现

:placeholder-shown伪类目前兼容性如下：

:placeholder-shown兼容性

直接上代码！☺️

源码

https://jsbin.com/qenucaz/edit?html,css,output

html:

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JS Bin</title>
</head>
<body>
  <div class="input-fill-box">
    <input class="input-fill" placeholder="邮箱" pattern="^[A-Za-z0-9\u4e00-\u9fa5]+@[a-zA-Z0-9_-]+(\.[a-zA-Z0-9_-]+)+$" required>
    <a href="javascript:" class="clear">close</a>
    <label class="input-label">邮箱</label>
</div>
</body>
</html>

css:

.input-fill{
  width: 100%;
  margin: 0;
  font-size: 16px;
  line-height: 1.5;
  outline: none;
  padding: 20px 16px 6px;
  border: 1px solid transparent;
   background: #f5f5fa;
  border-radius:10px;
  transition: border-color .25s;
}
.input-fill:placeholder-shown::placeholder {
    color: transparent;
     
}
.input-fill-box {
  width: 50%;
    position: relative;
}
.input-label {
    position: absolute;
    left: 16px; top: 14px;
    pointer-events: none;
    color:#BEC1D9;
   padding: 0 2px;
    transform-origin: 0 0;
    pointer-events: none;
    transition: all .25s;
}
.input-fill:not(:placeholder-shown) ~ .input-label,
.input-fill:focus ~ .input-label {
    transform: scale(0.75) translate(0px, -14px);    
}
.input-fill:focus{
  border: 2px solid #1d31aa;
}
 
.clear{
  position:absolute;
  top:10px;
  right:-20px;
   display: none;
    transition: all .25s;
}
.input-fill::-ms-clear { display: none; }
.input-fill:not(:placeholder-shown) + .clear { display: inline; }
 
.input-fill:valid {
 border-color: green;
 box-shadow: inset 5px 0 0 green;
}
.input-fill:not(:placeholder-shown):invalid {
 border-color: red;
 box-shadow: inset 5px 0 0 red;
}

 

 

 

 

 

 

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