html-css-js/iframe.html

<!doctype html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <!-- The above 3 meta tags *must* come first in the head; any other head content must come *after* these tags -->
    <title>Modern Web Apps</title>
    <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>

  </head>
  <body>
    <div>
      <div style="height:80vh; width:33%; background-color: blue; flex-direction: vertical;float:left">
      </div>
      <div style="height:80vh; width:33%; background-color: white; flex-direction: vertical;float:left">
      </div>
      <div style="height:80vh; width:33%; background-color: red; flex-direction: vertical;float:left">
      </div>
      <div style="width:100%; height:20vh">
        <iframe src="https://www.cs.utexas.edu" style="width:100%">
        </iframe>
      </div>
    </div>
  </body>
</html>