fix: use css vars for font size (wallet button)

[ryanpwaldon]

Description

Updated WalletButton font-size to use css vars instead of a hardcoded value.

• Resolves font-size overwriting #2060
• Bumped core version from 2.21.2 → 2.21.3-alpha.1
• Bumped core version for dependents
  • packages/demo
  • packages/react
  • packages/vue
  • packages/solid

Checklist

• Increment the version field in package.json of the package you have made changes in following semantic versioning and using alpha release tagging
• Check the box that allows repo maintainers to update this PR
• Test locally to make sure this feature/fix works
• Run yarn check-all to confirm there are not any associated errors
• Confirm this PR passes Circle CI checks
• Add or update relevant information in the documentation