<html>
<header>
<style>
ul {
display: flex;
position: absolute;
width: 800px;
top: 50%;
left: 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-type: 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;
}
li:hover ~ li::before {
left: 0;
}
li:active {
background: #000;
color: #fff;
}
</style>
</header>
<body>
<ul>
<li>不可思议的CSS</li>
<li>导航栏</li>
<li>光标下划线跟随</li>
<li>PURE CSS</li>
<li>Coco</li>
</ul>
</body>
</html>