<html><title>W3.CSS</title><meta name="viewport" content="width=device-width, initial-scale=1"><link rel="stylesheet" href="https://www.w3schools.cn/w3css/4/w3.css"><body class="w3-container w3-auto"><h2>显示警告</h2><p>w3-panel 类可用于显示警告：</p><div class="w3-panel w3-pale-yellow w3-border"> <h3>警告！</h3> <p>Yellow often 指示可能需要注意的警告。</p></div><div class="w3-panel w3-yellow w3-border"> <h3>警告！</h3> <p>Yellow often 指示可能需要注意的警告。</p></div></body></html>