直接上代码：
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title></title> <style type="text/css"> ul { display: flex; position: absolute; width: 1000px; top: 50%; left: 50%; -webkit-transform: translate(-50%, -50%); transform: translate(-50%, -50%); } li { position: relative; padding: 20px; font-size: 24px; color: #000; line-height: 1; transition: 0.2s all linear; cursor: pointer; list-style: none; } li::before { content: ""; position: absolute; top: 0; left: 100%; width: 0; height: 100%; border-bottom: 2px solid #000; transition: 0.2s all linear; } li:hover::before { width: 100%; top: 0; left: 0; transition-delay: 0.1s; border-bottom-color: #000; z-index: -1; } li:hover~li::before { left: 0; } li:active { background: #000; color: #fff; } </style> </head> <body> <div> <ul> <li>不可思议的CSS</li> <li>导航栏</li> <li>光标小下划线跟随</li> <li>PURE CSS</li> <li>Nav Underline</li> </ul> </div> </body> </html>