JSFiddle - React, Tailwind, and code Playground

HTML

<div id="maincontainer">
    <div id="topsection">
        <div class="innertube">
            <h1>CSS Fixed Layout #2.2- (Fixed-Fixed)</h1>
        </div>
    </div>
    <div id="content-container">
        <div id="contentwrapper">
            <div id="contentcolumn">
                <div class="innertube">content here</div>
            </div>
        </div>
    </div>
    <div id="rightcolumn">
        <div class="innertube">content here</div>
    </div>
</div>
<div id="footer"><a href="#">UIasdfg</a>
</div>
</div>

CSS

body {
       margin:0;
       padding:0;
       line-height: 1.5em;
       background:#f7f7f7;
   }
   b {
       font-size: 110%;
   }
   em {
       color: red;
   }
   #maincontainer {
       width: 1000px;
       /*Width of main container*/
       margin: 0 auto;
       /*Center container on page*/
   }
   #topsection {
       background: #f0f0f0;
       height: 90px;
       /*Height of top section*/
   }
   #topsection h1 {
       margin: 0;
       padding-top: 15px;
   }
   #content-container {
       float:left;
       width:100%;
       background:#f8f8f8;
       border:1px solid #f0f0f0;
       margin-top:-22px;
       margin-left:-1px;
       height:auto;
   }
   #contentwrapper {
       float: left;
       width: 100%;
   }
   #contentcolumn {
       margin-right: 310px;
       /*Set right margin to RightColumnWidth*/
       background:none;
       padding:15px;
       clear:both;
   }
   #rightcolumn {
       float: left;
       width: 310px;
       /*Width of right column*/
       margin-left: -311px;
       /*Set left margin to -(RightColumnWidth) */
       background: none;
       padding-top:20px;
       margin-top:1px;
       border-left:1px solid #222222;
   }
   #rightcolumn h2 {
       font:18px georgia;
       font-weight:bold;
       border-bottom:2px solid #222222;
   }
   #footer {
       clear: left;
       width: 100%;
       background: black;
       color: #FFF;
       text-align: center;
       padding: 4px 0;
   }
   #footer a {
       color: #FFFF80;
   }
   .innertube {
       margin: 10px;
       /*Margins for inner DIV inside each column (to provide padding)*/
       margin-top: 0;
   }
   body {
       margin:0;
       padding:0;
       line-height: 1.5em;
       background:#f7f7f7;
   }
   b {
       font-size: 110%;
   }
   em {
       color: red;
   }
   #maincontainer {
       width: 1000px;
       /*Width of main container*/
       margin: 0 auto;
       /*Center container on page*/
   }
   #topsection {
       background:...