test: fix failing specs due to missing CSS Custom Prop

[ju-Skinner]

Description

Icon specs were failing due to missing CSS Custom Property

Fixes #(issue)

Type of change

• Test

How Has This Been Tested?

• unit tests

Checklist:

If not applicable, leave options unchecked.

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing tests pass locally with my changes
• Design has QA'ed and approved this PR

[pixelflips]

LGTM!

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