VOTE-2334: Accessibility controls border contrast

[mlloydbixal]

Jira ticket

VOTE-2334

Description

Changes border color variables to be WCAG compliant. Also gives buttons z-index on hover to bring focus outline forward.

Deployment and testing

Post-deploy steps

1. lando retune
2. npm run build
3. toggle accessibility buttons
4. confirm contrast

QA/Testing instructions

1. Insert steps to test and confirm the result meets the "definition of done".

Checklist for the Developer

• A link to the JIRA ticket has been included above.
• No merge conflicts exist with the target branch.
• Automated tests have passed on this PR.
• A reviewer has been designated.
• Deployment and testing steps have been documented above, if applicable.

Checklist for the Peer Reviewers

• The file changes are relevant to the task objective.
• Code is readable and includes appropriate commenting.
• Code standards and best practices are followed.
• QA/Test steps were successfully completed, if applicable.
• Applicable logs are free of errors.