feat: CSS other-session-selected.

[holloway]

Makes other selected sessions stand out more with CSS tweak.

Note that the following screenshot has the middle truncated... CSS change is the border of the right 'lamps' box.

fixes #8525

[flynnliz]

This would work for me, thanks very much!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.88%. Comparing base (e33a1a8) to head (44e795d).
Report is 11 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8529      +/-   ##
==========================================
+ Coverage   88.81%   88.88%   +0.06%     
==========================================
  Files         312      312              
  Lines       40856    40891      +35     
==========================================
+ Hits        36288    36347      +59     
+ Misses       4568     4544      -24     

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