The new actions layout fixes regressed the stacking of menus from the

top header bar. rb-c-actions is now a flexbox, which changed the logic

for stacking contexts, causing menus to appear above other

higher-stacked items (such as the dashboard).
The core problem was that the header area was supposed to have its own

stacking context, but didn't have a suitable position for it. Now it

does, allowing the z-index to apply.
Note that this isn't perfect. Anything with a z-index higher than 50

(the value set for the header) will end up sitting on top of any menus

opened from this header. Due to the way stacking contexts are currently

created, solving this in a broader way ends up being a larger task, one

not tackled in this change.
There is a side effect from this change, in that the logo and other

parts of the branding section end up nudged to the right a few pixels.

We compensate for that by removing the extra left padding on the header.

Tested the Follow menu on the dashboard page. Verified that it appeared

above the dashboard.