comprehensive-rust/theme/css/redbox.css

div#aspect-ratio-helper {
  position: fixed;
  top: 8px;
  left: 8px;
  right: 8px;
  z-index: 1000;
  pointer-events: none;
}

div#aspect-ratio-helper div {
  outline: 3px dashed red;
  margin: 0 auto;
  /* At this width, the theme fonts are readable in a 16
       person conference room. If the browser is wider, the
       text becomes too small to be legible. */
  max-width: 980px;
  /* On a standard 16/9 monitor, we expect to lose a bit
       of vertical space to borders. */
  aspect-ratio: 16/8.5;
}

#instructor-menu-list {
  margin-left: 55px;
}