[Enhancement] Checkbox - Selected state color contrast

[henrikvoetmand]

• I have written a good issue

Describe the enhancement

Selected state color contrast ratio 3:1 against the background

Describe the solution you'd like

Have you considered any alternatives?

Are there any additional context?

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Checklist:

The following tasks should be carried out in sequence in order to follow the process of contributing correctly.

Refinement

• Request that the issue is UX refined
• Request that the issue is tech refined; do not proceed until this is done.

Implementation

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• Make sure you have read: "Before you get coding".
• Signal to others you are working on the issue by assigning yourself.
• Create a branch from the develop branch following our branch naming convention.
• Publish a WIP implementation to Github as a draft PR and ask for feedback.
• Make sure you have implemented tests following the guidelines in: "The good: Test".
• Update the cookbook with examples and showcases.

Review

Once the issue has been implemented and is ready for review:

• Do a self-review.
• Create a pull-request. If you created a draft PR during implementation you can just mark that as "ready for review".