JSFiddle - React, Tailwind, and code Playground

HTML

<div class="menu" id="topMenu">
    
    <div id="topMenuSlider"></div> <!-- Red Sliding Background-->
    
    <div class="menuItem" id="menu_index">
        <a href="/index.php">Home</a>                    
    </div>

    <div class="menuItem" id="menu_howitworks">
        <a href="/howitworks.php">How it Works</a>                    
    </div>

    <div class="menuItem" id="menu_benefits">
        <a href="/benefits.php">Benefits &amp; Savings</a>                    
    </div>

    <div class="menuItem" id="menu_quote">
        <a href="/quote.php">Request a Quote</a>                    
    </div>    
    
    <div class="menuItem" id="menu_dealers">
        <a href="/dealers.php">Dealer Information</a>                    
    </div>    

</div>

CSS

div.menu{
    font-family: verdana;
    font-size:13px;
    width:1100px;
    height:29px;
    color:#fff;
    text-align: left;
    padding: 6    px 0px 0px 8px;
    margin: 0px 0px 0px 0px;
    border 1px dashed #000;
    overflow:hidden;
}
.menu .highlight{color:#0ff}
.menu a:link {color:#00f; text-decoration: none}
.menu a:visited {color:#00f; text-decoration: none}
.menu a:active {color:#00f; text-decoration: none}
.menu a:hover {color:#00f; text-decoration: underline;}
.menu a.utilLink{font-family:verdana; font-size:10px;}


.menuItem{
    margin-right:20px;
    font-family: verdana;
    font-size:11px;
    font-weight:bold;
    color:#fff;    
    display:inline;
    cursor:pointer;
    height:25px;
}
#topMenu{
    overflow:hidden;
        
}
#topMenuSlider{
    -moz-border-radius:5px;
    -webkit-border-radius:5px;    
    background:#ff0000;
    filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#ff0000', endColorstr='#ff3333'); /* for IE */
    background: -webkit-gradient(linear, left top, left bottom, from(#ff0000), to(#000000)); /* for webkit browsers */
    background: -moz-linear-gradient(top,  #ff0000,  #000000); /* for firefox 3.6+ */
    position:absolute;    
}

JavaScript

var item = $('#menu_index');
$('#menuItem').css({
    'z-index:': '9999'
});
$('#topMenuSlider').css({
    'top' : (item.position().top -5) + 'px',
    'left' : (item.position().left-5) + 'px',
    'width' : (item.width()+10) + 'px',
    'height' : (item.height()+10) + 'px',
    'z-index:': 'auto'
});