JSFiddle - React, Tailwind, and code Playground

HTML

<ul id="navi" class="nav navbar-nav">
              <li class="current_page_item"><a href="" onfocus="this.blur()">Startseite</a></li>
              <li><a href="ueber-uns/" onfocus="this.blur()">Über Uns</a></li>
              <li class="dropdown">
                <a href="#" class="dropdown-toggle" data-toggle="dropdown">Dienstleistungen <b class="caret"></b></a>
                
              </li>
              <li><a href="referenzen/" onfocus="this.blur()">Referenzen</a></li>
              <li><a href="kontakt/" onfocus="this.blur()">Kontakt</a></li>
            </ul>

CSS

#navi { 
	margin: 0 auto; 
	list-style: none; 
	position: relative; 
	width: 960px; 
}
#navi li { 
	display: inline-block;
}
#navi li a { 
	color: #bbb; 
	font-size: 14px; 
	float: left;
	padding: 6px 10px 4px 10px;
	text-decoration: none;
	text-transform: uppercase;
}
#navi li a:hover { 
	color: white; 
}
#magic-line { 
	position: absolute;
	bottom: -2px; 
	left: 0; 
	width: 100px; 
	height: 2px; 
	background: #fe4902;
}

JavaScript

$(function() {
    
	var $el, leftPos, newWidth;
	
    $("#navi").append("<li id='magic-line'></li>");
    var $magicLine = $("#magic-line");
    
    $magicLine
        .width($(".current_page_item").width())
        .css("left", $(".current_page_item a").position().left)
        .data("origLeft", $magicLine.position().left)
        .data("origWidth", $magicLine.width());
        
    $("#navi li").find("a").hover(function() {
        $el = $(this);
        leftPos = $el.position().left;
        newWidth = $el.parent().width();
        
        $magicLine.stop().animate({
            left: leftPos,
            width: newWidth
        });
    }, function() {
        $magicLine.stop().animate({
            left: $magicLine.data("origLeft"),
            width: $magicLine.data("origWidth")
        });    
    });
});