<!DOCTYPE html>
<html>
  <head>
    <style>
      /* Page is expected to be exactly 800x600 */
      html, body {
        width: 800px;
        height: 600px;
        margin: 0;
        overflow: hidden;

        display: flex;
        flex-flow: column nowrap;
        justify-content: space-around;
        align-items: stretch;
      }

      .row {
        display: flex;
        flex-flow: row nowrap;
        justify-content: space-around;
        align-items: center;
      }
      .row.rounding-0 > .box 