feat: Update CSS variables with new tokens

[brianacnguyen]

Description

This PR

• updated the css variables with new tokens
• updated the migration docs with critical changes

Related issues

Fixes: https://github.com/MetaMask/design-tokens/issues/687

Manual testing steps

1. Go to storybook
2. Checkout colors

Screenshots/Recordings

Before

After

Pre-merge author checklist

• [x] I’ve followed MetaMask Coding Standards.
• [x] I've clearly explained what problem this PR is solving and how it is solved.
• [x] I've linked related issues
• [x] I've included manual testing steps
• [ ] I've included screenshots/recordings if applicable
• [ ] I’ve included tests if applicable
• [x] I’ve documented my code using JSDoc format if applicable
• [x] I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.
• [x] I’ve properly set the pull request status:
  • [ ] In case it's not yet "ready for review", I've set it to "draft".
  • [ ] In case it's "ready for review", I've changed it from "draft" to "non-draft".

Pre-merge reviewer checklist

• [ ] I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• [ ] I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

[metamaskbot]

Builds ready [11b2131]

Storybook: Storybook

[metamaskbot]

Builds ready [c9d5dad]

Storybook: Storybook

[metamaskbot]

Builds ready [91cc421]

Storybook: Storybook

[metamaskbot]

Builds ready [3635e45]

Storybook: Storybook

[metamaskbot]

Builds ready [bf2ab80]

Storybook: Storybook

[metamaskbot]

Builds ready [babc482]

Storybook: Storybook

[metamaskbot]

Builds ready [339f7e4]

Storybook: Storybook

[metamaskbot]

Builds ready [d52a01f]

Storybook: Storybook