fix: selected ghost button higlighting

[djbarnwal]

Adds selected state CSS for chart type selector button icons

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!

[djbarnwal]

Merging as this is a CSS change and test failures are unrelated