Underline bar renderable

[darrenburns]

Naming is hard :) more than happy to hear suggestions for the params etc.

Closes #238

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (css@3574a6d). Click here to learn what that means.
The diff coverage is n/a.

@@          Coverage Diff           @@
##             css     #246   +/-   ##
======================================
  Coverage       ?   38.58%           
======================================
  Files          ?       82           
  Lines          ?     6240           
  Branches       ?        0           
======================================
  Hits           ?     2408           
  Misses         ?     3832           
  Partials       ?        0           

Flag	Coverage Δ
unittests	38.58% <0.00%> (?)

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[willmcgugan]

👍