JSFiddle - React, Tailwind, and code Playground by Tsuneo Yoshioka August 01, 2014 HTML <div id="wrapper"> <div id="header"> <img src="header_image.svg" alt="the img is empty"/> </div> <div id="content"> Some content <button onclick="AddContent()">click me to enlarge the header</button > </div> </div> CSS html, body { height: 100%; margin: 0px; } #wrapper:before { content:''; float: left; height: 100%; } #wrapper { height: 100%; background-color: black; color: white; } #header { background-color:#000; } #content { background-color: gray; } #content:after { content:''; display: block; clear: both; } JavaScript function AddContent() { $("<div>More content</div>").appendTo($("#header")); }