JSFiddle - React, Tailwind, and code Playground

HTML

<div id="wrapper">
    <div id="one">bgfgf</div>
    <div id="two">
        <iframe width="100%" height="100%" src="abc.html"></iframe>
    </div>
  </div>
</div>

CSS

#wrapper {height:350px; width:300px; border:3px solid gray; display:table;}
#one {height:100px; background-color:red;display: table-row;}
#two {background-color:blue;display: table-row; position: relative;}
iframe {background:white;-webkit-box-sizing:border-box; -moz-box-sizing:border-box; box-sizing:border-box;
    position: absolute;
    left: 0px;
    right: 0px;
    top: 0px;
    bottom: 0px;
}