index.css

body {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  position: relative;
  height: 100vh;
  width: 100vw;
  display: block;
  overflow: hidden;
  background: #666666;
}

.fullscreen {
  position: absolute;
  height: 100vh;
  width: 100vw;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
}

.iframe {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  border: 0;
  z-index: 2;
}