There are several elements that are practically invisible though: play/pause buttons on the sides, comments in parentheses, explanatory text on graphics.
It's a shame because otherwise the presentation is really good.
The play/pause buttons are meant to not disturb the reading. They are only for the rare occasions when you want to pause the video to examine it closer.
Comments can be hovered over to make them fully visible.
It's a shame because otherwise the presentation is really good.