:required
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
尝试一下
label { display: block; margin-top: 1em; } .req { color: red; } *:required { background-color: gold; } <form> <label for="name">Name: <span class="req">*</span></label> <input id="name" name="name" type="text" required /> <label for="birth">Date of Birth:</label> <input id="birth" name="birth" type="date" /> <label for="origin" >How did you find out about us? <span class="req">*</span></label > <select id="origin" name="origin" required> <option>Google</option> <option>Facebook</option> <option>Advertisement</option> </select> <p><span class="req">*</span> - Required field</p> </form> 这个伪类很有用，可以突出显示在提交表单之前必须具有有效数据的字段。
备注： :optional 伪类选择可选表单字段。
语法
css
:required { /* ... */ } 示例
必填字段具有红色边框
HTML
html
<form> <div class="field"> <label for="url_input">Enter a URL:</label> <input type="url" id="url_input" /> </div> <div class="field"> <label for="email_input">Enter an email address:</label> <input type="email" id="email_input" required /> </div> </form> CSS
css
label { display: block; margin: 1px; padding: 1px; } .field { margin: 1px; padding: 1px; } input:required { border-color: #800000; border-width: 3px; } input:required:invalid { border-color: #c00000; } 结果
无障碍考虑
规范
| Specification |
|---|
| HTML # selector-required |
| Selectors Level 4 # required-pseudo |