<html><head><style> label { display: block; margin-top: 10px;}input:checked { outline: 1px solid red;}</style></head><body><h1>:checked 伪类演示</h1><form><p>选择性别:</p><label><input name="gender" type="radio" value="male" checked> 男</label><label><input name="gender" type="radio" value="female"> 女</label><p>选择交通工具:</p><label><input name="bike" type="checkbox" checked>我有自行车</label><label><input name="car" type="checkbox">我有汽车</label> </form></body></html>