JSFiddle - React, Tailwind, and code Playground
HTML
<div id="maincontainer">
</div>
<br/>
<select onchange="changecolor();">
<option>Blue</option>
<option>Green</option>
<option>Red</option>
</select>
CSS
#maincontainer
{
background-color:blue;
width:100px;
height:100px;
display:block;
}
JavaScript
function changecolor(){
var color= $("select").val();
$("#maincontainer").hide().css("background-color",color).fadeIn();
}