JSFiddle - React, Tailwind, and code Playground

HTML

<div id="div1">
<ul>
   <li id="div2"><div>div2</div></li>
   <li id="div3"><div>div3</div></li>
</ul>
</div>

CSS

#div1 {  border:1px solid red; overflow:hidden;  }
    #div1 ul {  list-style-type:none; margin:0; padding:0; display:table; width:100%;  }
    #div1 li {  display:table-cell;  }
    #div2 {  background-color:pink; width:100%; height:40px;  }
    #div3 {  background-color:yellow; width:40px; height:40px;  }