Yup, that's on me. As noted elsewhere this was my first attempt at converting Keynote slides into HTML (using https://github.com/mcfunley/better-keynote-export). I've pushed a fix for the overflow.
This presentation was more about industry trends than GitHub specifically. My point here is that as time in apps becomes a greater portion of the average user's time on the internet, the more poorly-built web experiences will stick out.
No kidding! This is my first time experimenting with converting Keynote slides into HTML, so I'm not surprised it didn't go perfectly. I just pushed a quick fix for the overflow issue but should probably figure out a longer-term solution.