fix(a11y): fixing accessibility on Window High Contrast Mode

[rjhenriquez]

Closes #6888

Fixing Overflow menu accessibility on Window High Contrast Mode

Changelog

Changed

Overflow Menu component

Testing / Reviewing

On a Windows 10 machine, go to settings --> ease of access --> high contrast and flick the switch. Compare the storybook in Edge (Should be in High Contrast) to Chrome (Should look normal).
For Firefox, you'll need to open it up and type about:config into the address bar. Then, search for layout.css.prefers-contrast and set it to true.

• Visit Multiselect component
• Verify that there is a focus state on the multiselect
• Verify that the options have a highlight state
• Verify that the options have a focus state

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