JSFiddle - React, Tailwind, and code Playground

HTML

<div id="wrapper">
     <div class="top-tab">
         <div class="top-tab-box"></div>
         <div class="top-tab-box"></div>
         <div class="top-tab-box"></div>
         <!-- don't use a div for .clear-->
<span class="clear"></span>
    </div>

CSS

.top-tab-box
{
   width: 200px;
   height: 200px;
   background: #000;
   float: left;
   margin: 10px;

}
.clear {clear:both;display:block;}
/*use :last-of-type instead of :last-child*/
.top-tab div:last-of-type{
   background: #e7e7e7;
}