[TFL] Added 2px outline off-set for focus state for TFL button

[lucascumsille]

Fixes: https://github.com/mysociety/societyworks/issues/4188
This allows that the outline has enough contrast with the background color.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.61%. Comparing base (aa389eb) to head (3267975).
Report is 1 commits behind head on master.

❗ Current head 3267975 differs from pull request most recent head 8f8d37b. Consider uploading reports for the commit 8f8d37b to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4878   +/-   ##
=======================================
  Coverage   82.60%   82.61%           
=======================================
  Files         387      387           
  Lines       30461    30458    -3     
  Branches     4809     4809           
=======================================
  Hits        25162    25162           
+ Misses       3847     3845    -2     
+ Partials     1452     1451    -1     

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