滑动菜单实现

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>index</title>
    <style>
        nav {
            --position: 0;
            --bgH: 10%;
            --bgY: bottom;
            --activeBg: '';
            position: relative;
            margin: 70px auto 0;
            width: 582px;
            height: 50px;
            transition: background-position .4s;
            background: linear-gradient(to right, lightskyblue 20%, transparent 0), linear-gradient(#34495e,#34495e);
            background-size: 100% var(--bgH), 100% 100%;
            background-repeat: no-repeat, no-repeat;
            background-position: var(--position) var(--bgY), 0 0;
            border-radius: 8px;
            font-size: 0;
            box-shadow: 0 3px 10px 0 rgba(0, 0, 0, .3);
            display: flex;
        }
        nav a {
            color: #fff;
            font-size: 20px;
            text-decoration: none;
            flex: 1;
            display: flex;
            justify-content: center;
            align-items: center;
        }
        nav a:hover{
            background-color: lightblue;
        }
        nav a.active{
            background-color: linear-gradient(var(--activeBg));
            background-size: 100% var(--bgH);
        }
        nav a:first-child{
            border-top-left-radius: 8px;
            border-bottom-left-radius: 8px;
        }
        nav a:last-child{
            border-top-right-radius: 8px;
            border-bottom-right-radius: 8px;
        }
    </style>
</head>
<body>
    <nav>
        <a href="#" active>主页</a>
        <a href="#">博客</a>
        <a href="#">随笔手记</a>
        <a href="#">关于此</a>
        <a href="#">联系</a>
    </nav>
    <script>
        let nav = document.querySelector('nav');
        let navW = nav.offsetWidth;

        nav.addEventListener('click', e => {
            nav.style.setProperty('--activeBg', '')

            let children = Array.from(nav.children)
            children.forEach(t => t.classList.remove('active'))
            e.target.classList.add('active')

            let index = children.indexOf(e.target);
            //获取相对位置简便方法？？？？？
            let w = navW/5 * index;
            nav.style.setProperty('--position', w + "px")
        })

        nav.addEventListener('transitionend', e => {
            nav.style.setProperty('--activeBg', 'lightskyblue')
        })
    </script>
</body>
</html>