Use compound colours for verification badges

[kerryarchibald]

• Update e2e- style variables to use compound red and green
• Use e2e variables for shield styles

Before:

After:

No visual change:

Checklist

• Tests written for new code (and old code if feasible)
• Linter and other CI checks pass
• Sign-off given on the changes (see CONTRIBUTING.md)

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This change is marked as an internal change (Task), so will not be included in the changelog.