:optional

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since ⁨2015年7月⁩.

:optional CSS 伪类表示任何未设置 required 属性的 <input>、<select> 或 <textarea> 元素。

尝试一下

label { display: block; margin-top: 1em; } .req { color: red; } *:optional { background-color: palegreen; }

<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，可以为不是必须提交的表单字段设置样式。

备注：:required 伪类选择必填表单字段

语法

css

:optional { /* ... */ }

示例

可选字段具有紫色边框

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:optional { border-color: rebeccapurple; border-width: 3px; }