<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><div class="w3-container"> <br> <div class="w3-container w3-border-bottom"> <p>w3-border-bottom 类向元素添加底部边框。</p> </div></div></body></html>