html, body {
  width: 100%;
  height: 100%;
  margin: 0;      /* important */
  padding: 0;     /* important */
  font-family: Helvetica, sans-serif;
}

#arbox {
  width: 100%;
  height: 100%;
  border: 0;
  border-radius: 5px;
  background: #fff;
  box-sizing: border-box;
}

model-viewer {
  width: 100%;
  height: 100%;
  display: block; /* avoids inline-element whitespace issues */
}