Flash of dark theme in rustdoc

[ruuda]

Currently, for every page I load on https://doc.rust-lang.org/std, there is a “flash of dark theme” for almost a second, as you can see in this timeline:

Furthermore, the entire docs load very slowly, even with a primed cache. (You can also see fonts kicking in very late.) I suspect part of the reason is that all resources are served with cache-control: max-age=0, no-store, no-cache, must-revalidate, including fonts and style sheets. I don’t know if this is done on purpose because the docs are updated frequently? If so, using an etag would probably be a better solution.

[ruuda]

I can only reproduce this in Chromium, not in Firefox.

[varkor]

This is a duplicate of #49648. The bug has been fixed, but the fix will unfortunately take a little time to get into the live version of the docs!