bigbluebutton-Github/bigbluebutton-html5/imports/ui/components/presentation/presentation-close-button/styles.scss

.button {
  z-index: 1;
  position: absolute;
  top: 0;
  right: 0;
  left: auto;
  cursor: pointer;

  [dir="rtl"] & {
    right: auto;
    left :0;
  }
}