Improve color contrast of the focus ring

[connor-baer]

Addresses DSYS-443.

Purpose

Circuit UI's focus ring doesn't meet contrast requirements (1:1.11).

Before

After

Approach and changes

• Darken the --cui-border-focus and colors.border.focus design tokens
• Reduce the thickness of the focus ring and offset it from the focused element

Definition of done

• Development completed
• Reviewers assigned
• Unit and integration tests
• Meets minimum browser support
• Meets accessibility requirements

[changeset-bot]

🦋 Changeset detected

Latest commit: ab2f8b7

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 6 packages

Name	Type
@sumup/design-tokens	Minor
@sumup/circuit-ui	Major
@sumup/eslint-plugin-circuit-ui	Major
@sumup/stylelint-plugin-circuit-ui	Major
@sumup/astro-template-circuit-ui	Patch
@sumup/remix-template-circuit-ui	Patch

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Name	Status	Preview	Comments	Updated (UTC)
oss-circuit-ui	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Nov 14, 2023 3:58pm

[codecov]

Codecov Report

Merging #2296 (ab2f8b7) into main (c776399) will increase coverage by 0.00%.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2296   +/-   ##
=======================================
  Coverage   97.15%   97.15%           
=======================================
  Files         251      251           
  Lines       19862    19864    +2     
  Branches     1224     1224           
=======================================
+ Hits        19297    19299    +2     
  Misses        551      551           
  Partials       14       14           

Files	Coverage Δ
packages/circuit-ui/styles/style-mixins.ts	98.26% <100.00%> (+0.01%)	⬆️
packages/design-tokens/themes/light.ts	100.00% <100.00%> (ø)