css实现一下点击input输入框后提示文字上移并缩小，这种表单美化挺常见的，效果如图：
代码如下：
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8"/>
<meta name="viewport"content="width=device-width, initial-scale=1">
<title></title>
<style>
.box{
width: 500px;
position: relative;
margin-top: 50px;
}
.box input{
outline: none;
border: none;
width: 100%;
padding: 10px 0;
color: #000;
font-size: 16px;
border-bottom: 1px solid red;
background: none;
}
.box label{
position: absolute;
top: 0;
left: 0;
color: #000;
font-size: 16px;
pointer-events: none;
transition: all 0.5s;
line-height: 38px;
}
.box input:focus + label,
.box input:valid + label{
font-size: 12px;
top: -20px;
color: red;
}
</style>
</head>
<body>
<div class="box">
<input type=""name=""id=""value=""required="required"/>
<label>name</label>
</div>
</body>
</html>
