<style>
  * { margin: 0; padding: 0; box-sizing: border-box; }
  html, body { width: 100%; height: 100%; overflow: hidden; }
  .iframe-fullscreen {
    position: fixed;
    top: 0;
    left: 0;
    width: 100vw;
    height: 100vh;
    border: none;
    display: block;
  }
</style>