At id.discourse.com, if one were to go to /t/1, it brings up a 404 page. However, all the text is white, as is the background of the notice, therefore rendering it invisible.
But it’s definitely there, upon inspection:
While I’m at it, the weird square at the bottom is filled with white. It has a fill property of value currentColor (which isn’t valid, I assume), but changing the fill property to black showed it:
