node_modules/video.js/src/css/components/_fullscreen.scss

.video-js .vjs-fullscreen-control {
  cursor: pointer;
  @include flex(none);
  & .vjs-icon-placeholder {
    @extend .vjs-icon-fullscreen-enter;
  }
}
// Switch to the exit icon when the player is in fullscreen
.video-js.vjs-fullscreen .vjs-fullscreen-control .vjs-icon-placeholder {
  @extend .vjs-icon-fullscreen-exit;
}