<!DOCTYPE html>
<html>
  <head>
    <title>custom_size</title>
    <link rel="icon" href="data:,">
    <style>
      html {
        width: 100%;
        height: 100%;
      }

      body {
        /*
          deal with the default Chrome margins
          https://source.chromium.org/chromium/chromium/src/+/master:third_party/blink/renderer/core/html/resources/html.css;
        */
        margin: 0;
      }

      .spacer {
        width:  1272px;
        height: 1008px;
      }
    </style>
  </head>
  <body>
    <div class="spacer"></div>
  </body>
</html>
