packages/react-devtools-shell/multi.html

<!doctype html>
<html>
  <head>
    <meta charset="utf8">
    <title>React DevTools</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <style>
      * {
        box-sizing: border-box;
      }
      body {
        display: flex;
        flex-direction: row;
        position: absolute;
        top: 0;
        left: 0;
        right: 0;
        bottom: 0;
        margin: 0;
        padding: 0;
        font-family: -apple-system, BlinkMacSystemFont, Segoe UI, Helvetica, Arial,
          sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol;
        font-size: 12px;
        line-height: 1.5;
      }
      .column {
        display: flex;
        flex-direction: column;
        flex: 1 1 50%;
      }
      .column:first-of-type {
        border-right: 1px solid #3d424a;
      }
      .iframe {
        height: 50%;
        flex: 0 0 50%;
        border: none;
      }
      .devtools {
        height: 50%;
        flex: 0 0 50%;
      }
    </style>
  </head>
  <body>
    <div class="column left-column">
      <iframe id="iframe-left" class="iframe"></iframe>
      <div id="devtools-left" class="devtools"></div>
    </div>
    <div class="column">
      <iframe id="iframe-right" class="iframe"></iframe>
      <div id="devtools-right" class="devtools"></div>
    </div>

    <script src="dist/multi-devtools.js"></script>
  </body>
</html>