JSFiddle - React, Tailwind, and code Playground

HTML

<div id="mainContainer">
    <div id="leftContent">

    </div>

    <div id="rightContent">

    </div>
    <div style="clear: both;"></div>
</div>

CSS

#mainContainer{
    width: 1000px;
    /* height: 1000px; */
    height:auto;
    margin-left:auto;
    margin-right:auto;
    background-color: #ff0000;
    padding-bottom: 20px;
}
#leftContent{
    height: 100px;
    float: left;
    width: 380px;
    background-color: violet;
}
#rightContent{
    height: 100px;
    float: right;
    width: 620px;
    background-color: yellow;
}