banner breaks positions for other elements

[shcheklein]

After we introduced the banner we broke a few things:

[rogermparent]

I'm almost done with a fix for this, mostly revolving around making the placeholder grow and shrink while considering the extra height the banner adds.

I originally wanted to move the hamburger icon into the header so it could be vertically centered with position: absolute, but then found due to z-index issues we would have to sacrifice the "moving button lines" effect that requires one element to be the button in both the header and overlay menu. While it's a trade-off I'd take personally, I decided to opt for keeping all existing functionality by default.