New docs are hostile on bad connections

[richo]

On terrible cafe wifi, the docs are unusable, see this screenshot:

Highlighting text I was able to assert that it had actually loaded, but while I was waiting on my connection to load stylesheets, it was all white-on-white.

[brson]

I've noticed this too and it's icky.

cc @thehydroimpulse @adridu59

[richo]

There's some follow-up discussion about how to make this better when building offline docs here, but would also be great if this were nicer on the hosted ones

[steveklabnik]

This is basically the same as #19257 , and while it's newer, it has a lot more info, so I'm giving it a close.