js/html/menu.html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Menu</title>
    <style>
        /* 表现样式 */

        .multi_drop_menu {
            font: 1em helvetica, arial, sans-serif;
        }

        .multi_drop_menu a {
            display: block;
            color: #555;
            background-color: #eee;
            padding: .2em 1em;
            border-width: 3px;
            border-color: transparent;
        }

        .multi_drop_menu a:hover {
            color: #fff;
            background-color: #aaa;
        }

        .multi_drop_menu a:active {
            background: #fff;
            color: #ccc;
        }

        .multi_drop_menu li ul {
            width: 9em;
        }

        .multi_drop_menu li li a {
            border-right-style: none;
            border-top-style: solid;
        }

        /* 功能样式 */

        .multi_drop_menu * {
            margin: 0;
            padding: 0;
        }

        .multi_drop_menu ul {
            float: left;
        }

        .multi_drop_menu li {
            float: left;
            list-style-type: none;
            position: relative;
        }

        .multi_drop_menu li a {
            display: block;
            border-right-style: solid;
            background-clip: padding-box;
            text-decoration: none;
        }

        .multi_drop_menu li:hover>ul {
            display: block;
        }

        .multi_drop_menu li:hover>a {
            color: #fff;
            background-color: #aaa;
        }

        .multi_drop_menu li:last-child a {
            border-right-style: none;
        }

        .multi_drop_menu li ul {
            display: none;
            position: absolute;
            left: 0;
            top: 100%;
        }

        .multi_drop_menu li li {
            float: none;
        }

        .multi_drop_menu li li ul {
            position: absolute;
            left: 100%;
            top: 0;
        }
    </style>
</head>

<body>
    <nav class=" multi_drop_menu">
        <!--一级 开始 -->
        <ul>
            <li>
                <a href="#"> Power</a>
            </li>
            <li>
                <a href="#"> Money</a>
            </li>
            <li>
                <a href="#"> Love</a>
            </li>
            <li>
                <a href="#"> Fame</a>
                <!--二级 开始 -->
                <ul>
                    <li>
                        <a href="#"> Sports Star</a>
                    </li>
                    <li>
                        <a href="#"> Movie Star</a>
                    </li>
                    <li>
                        <a href="#"> Rock Star</a>
                        <!--三级 开始 -->
                        <ul>
                            <li>
                                <a href="#"> Bruce Springsteen</a>
                            </li>
                            <li>
                                <a href="#"> Bono</a>
                            </li>
                            <li>
                                <a href="#"> Mick Jagger</a>
                            </li>
                            <li>
                                <a href="#"> Bob Dylan</a>
                            </li>
                        </ul>
                        <!--三级 结束 -->
                    </li>
                    <li>
                        <a href="#"> Web Designer</a>
                    </li>
                </ul>
                <!--二级 结束 -->
            </li>
        </ul>
        <!--一级 结束 -->
    </nav>
</body>
</html>