Update the alternative login, verify email, and error boundary components to use css variables for colors

[sandymcfadden]

Fix

This is a continuation of moving to CSS variables for colors within the app.
This updates the Alternative Login, Email Verification, and Error Boundary components.

Test

The easiest way to test these is to force the modals to appear by temporarily editing the app.tsx file to always show them.
To display the error boundary you need to introduce an error in code.

• Smoke test in light and dark mode
• Compare between production and this branch
• Enable the Alternative Login Prompt
• Ensure it still looks the same
• Enable the Email Verification Modal
• Ensure it still looks the same
• Trigger the Error Boundary
• Ensure it still looks the same

Release

• Updated the Alternative Login, Email Verification, and Error Boundary components to use CSS variables for colors