1 to indicate that I also feel this to be an issue with MDN's interface. e.g. see this screenshot, where the actual gist of the illustrative examples - the repeat values - are hidden away:

To workaround, if I then try to increase the size of the window and maximize it, then something else happens - a new right scrollbar appears! and we're back where we started:

Giving an option to toggle the sidebar might be one solution. But I don't know what's the best solution, don't want to get into the solution space without understanding the nuances, just wanted to chip in to say that I also face the problem mentioned by OP.

(Thanks for MDN by the way if any contributors read this, such an amazing resource.)