chore: Include focus-visible styles in build output

[gethinwebster]

Issue #, if available:

Description of changes:

Ensure that styles as well as JS are included in build output for focus-visible.

TBC: if we end up with many more similar helpers that include CSS in the future then we might want to do this in a more automated way, but for now it seems a relatively rare occurrence.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.71%. Comparing base (9b718bb) to head (c78642f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #71   +/-   ##
=======================================
  Coverage   98.71%   98.71%           
=======================================
  Files          19       19           
  Lines         388      388           
  Branches       76       82    +6     
=======================================
  Hits          383      383           
  Misses          5        5           

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