Force consistent header height

[janbrasna]

One-line summary

Refreshed pages have different defaults affecting also nav elements, making shifts in layout visible when navigating to older pages. This sets the base var explicitly to the header components to not inherit any other value.

Significant changes and points to review

Both the desktop and mobile nav inconsistencies caused by differing line-height as captured in the tracking issue are resolved here by using the "taller" version as that seems to be better aligned in general.

Issue / Bugzilla link

Fixes #15788

Testing

/about/ ⇄ /products/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.10%. Comparing base (c8ac92f) to head (0fd6981).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15790      +/-   ##
==========================================
+ Coverage   79.07%   79.10%   +0.03%     
==========================================
  Files         160      160              
  Lines        8359     8371      +12     
==========================================
+ Hits         6610     6622      +12     
  Misses       1749     1749              

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