It seems that your notebook is missing a stylesheet, which causes many of the buttons to be end up empty. You can find an example with stylesheet in this notebook: https://observablehq.com/@joewdavies/procedural-gl-js#cell-61

fixed, thank you!

I wonder if the map style has changed, because I can barely make out land and see here. Both are in almost the same shade of dark blue.

works for me

Strange, it works for me now, too. Nevermind then!