fix: remove padding from borderless stat-tabs, extend varTheme

[jhoward-eightfold]

SUMMARY:

When turning off border for StatTabs, remove the padding as designers will most often want the tabs flush with the surrounding content.

Additional enhancements to varTheme support.

GITHUB ISSUE (Open Source Contributors)

JIRA TASK (Eightfold Employees Only):

CHANGE TYPE:

• Bugfix Pull Request
• Feature Pull Request

TEST COVERAGE:

• Tests for this change already exist
• I have added unittests for this change

TEST PLAN:

Visual inspection of StatTabs to ensure they render as desired.

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[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (main@3554159). Click here to learn what that means.
Patch has no changes to coverable lines.

Additional details and impacted files

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  Coverage        ?   84.99%           
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  Files           ?      749           
  Lines           ?    16047           
  Branches        ?     5495           
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  Hits            ?    13639           
  Misses          ?     2347           
  Partials        ?       61           

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