W3School TIY Editor
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<!DOCTYPE html> <html> <head> <style> form { border: 1px solid gray; color: gray; padding: 10px; } form:focus-within { border: 2px solid black; background-color: beige; color: black; } </style> </head> <body> <h1>:focus-within 实例</h1> <p>尝试在表单中输入内容：</p> <form> <label for="name">姓名：</label><br> <input id="name" name="name" type="text" /><br> <label for="email">邮箱：</label><br> <input id="email" name="email" type="email" /><br> <label for="country">国家：</label><br> <input id="country" name="country" type="text" /> </form> </body> </html>