<!DOCTYPE html>
<html>
  <head>
    <style>
      html {
        background-color: #ccc;
        font-size: 50px;
      }
      div.frame {
        text-align: center;
        float: left;
        width: 310px;
        height: 400px;
      }
      iframe {
        width: 300px;
        height: 300px;
        border: solid 1px black;
        display: block;
        background-color: white;
      }
    </style>
  </head>
  <body>
    <div></div>
    <div class="frame">
      <iframe id="frameone" sandbox="all