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>