Header goes offscreen when browser window is smaller than expected or default font size too large

[SkySkimmer]

This is the size of a new window on a fresh firefox profile on my machine:

Notice how "get started" gets cut off.

On my work profile I have vertical tabs and default font size 20 also causing it to be cut off even with a fullscreen browser window:

[SkySkimmer]

Also the install page looks pretty bad since the IDE section gets pushed under the install instructions but the IDE selector is on top

This is particularly confusing when following an old link like https://coq.inria.fr/user-interfaces.html

[mattam82]

The second part of the problem (IDE buttons) is fixed by 944e85c, but the first issue is still there.