Replace custom color variables with design system tokens

[aduth]

Why: So that we have a single source of truth for colors, to improve consistency and reduce confusion.

Largely, there should not be any meaningful differences from this change. However, to the above point about consistency, there are a few minor differences between our ad hoc colors and the design system:

Before	After	Usage
#e1ce28 ($yellow)	#f5d600 (warning)	IAL2 cancellation warning list Edit: Removed
#00bfe7 ($teal)	#00a2c4 (info)	Session timeout modal IAL2 forgot password warning list Edit: Removed
#5b616a ($gray)	#454545 (ink)	Form field text color

Reference: https://design.login.gov/utilities/color/

This retains existing styling for email templates, but those should ideally be updated to use design system tokens as well.

[nickttng]

LGTM.

Slightly off-topic: About the warning lists here, have there been any discussions about aligning these bullet points with the LGDS?

[aduth]

Slightly off-topic: About the warning lists here, have there been any discussions about aligning these bullet points with the LGDS?

Yeah, I think we've been generally moving away from them. I'd be happy to do it sooner than later, maybe even as part of this pull request.

For context, it would be these two lists:

[anniehirshman-gsa]

LGTM and I'm all for standardizing the bullet styles on those two pages as well!

[aduth]

👍 I removed all the color list variations in df2bd9d.

Screen	Before	After
IAL2 Cancel Confirm
IAL2 Cancelled
IAL2 Forgot Password

[anniehirshman-gsa]

LGTM! Thanks for confirming with the screenshots.

[aduth]

Spotted another, with IAL1 account creation cancellation, updated in 38b76e2:

Before	After

[anniehirshman-gsa]

Spotted another, with IAL1 account creation cancellation

LGTM also!