JSFiddle - React, Tailwind, and code Playground

HTML

<nav id="topmenu">
            <ul>
                <li class="level1">
                    <a href="#" class="level1"><span>item1</span></a>
                </li>
                <li class="level1">
                    <a href="#" class="level1"><span>item2</span></a>
                    <ul class="level2">
                        <li class="level2"><a href="#" class="level2"><span>item1</span></a></li>
                        <li class="level2"><a href="#" class="level2"><span>item2</span></a></li>
                        <li class="level2"><a href="#" class="level2"><span>item3</span></a></li>
                    </ul>
                </li>
                <li class="level1">
                    <a href="#" class="level1"><span>item3</span></a>
                    <ul class="level2">
                        <li class="level2"><a href="#" class="level2"><span>item1</span></a></li>
                        <li class="level2"><a href="#" class="level2"><span>item2</span></a></li>
                        <li class="level2"><a href="#" class="level2"><span>item3</span></a></li>
                        <li class="level2"><a href="#" class="level2"><span>item4</span></a></li>
                    </ul>
                </li>
                <li class="level1">
                    <a href="#" class="level1"><span>item4</span></a>
                    <ul class="level2">
                        <li class="level2"><a href="#" class="level2"><span>item1</span></a></li>
                        <li class="level2"><a href="#" class="level2"><span>item2</span></a></li>
                        <li class="level2"><a href="#" class="level2"><span>item3</span></a></li>
                        <li class="level2"><a href="#" class="level2"><span>item4</span></a></li>
                        <li class="level2"><a href="#" class="level2"><span>item5</span></a></li>
                    </ul>
                </li>
                <li class="level1">
                    <a href="#"...

CSS

#topmenu{
    width:940px;
    margin:0 auto;
    border:1px solid #dfdfdf;
    height: 68px;
    border-radius:3px;
    -moz-border-radius:3px;
    -webkit-border-radius:3px;
    overflow: hidden;
    background: #ececec;
}
    #topmenu > ul{
        height: 40px;
        background: rgb(117,117,117);
    }
    #topmenu .level1,
    #topmenu .level1 > span,
    #topmenu .level2,
    #topmenu .level2 > span{float: left}

    #topmenu a.level1{
        display: block;
        height: 40px;
        line-height: 40px;
    }
    #topmenu a.level1 > span{
        padding: 0 8px;
        font-size: 14px;
        color: #dddddd;
        overflow: hidden;
    }
    #topmenu a.level1 > span:hover{
        color: #343434;
        background: rgb(156,214,226);
        background: url(data:image/svg+xml;base64,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);
        background: -moz-linear-gradient(top,  rgba(156,214,226,1) 0%, rgba(133,193,212,1) 50%, rgba(107,168,188,1) 50%, rgba(109,176,200,1) 55%, rgba(81,148,182,1) 100%);
        background: -webkit-gradient(linear, left top, left bottom, color-stop(0%,rgba(156,214,226,1)),...

JavaScript

$('#topmenu li.level1').hover(function(){

            $(this).find('ul.level2').stop(true,true).animate({
                opacity:"show"
            });
        }
    );