fix: move data attribute to light theme variables

[georgewrmarshall]

Description

This PR addresses a critical issue where the data-theme="light" attribute was incorrectly applied only to brand variables, resulting in the light mode theme not being activated correctly across all theme variables. The change ensures that the data-theme="light" attribute now correctly influences all relevant theme variables, ensuring a consistent and accurate representation of the light mode across the application.

Reason for Change

The light mode theme was not being applied correctly due to the data-theme="light" attribute being limited to brand variables. This led to inconsistencies in the UI where certain elements did not reflect the intended light mode appearance.

Improvement/Solution

By moving the data-theme="light" attribute to affect all theme variables, we ensure a uniform application of the light mode theme across the application, enhancing the user experience and visual consistency.

Related issues

Fixes: #626

Manual testing steps

Same as here #627

Screenshots/Recordings

Same as #627

Pre-merge author checklist

• I’ve followed MetaMask Coding Standards.
• I've clearly explained what problem this PR is solving and how it is solved.
• I've linked related issues.
• I've included manual testing steps.
• I've included screenshots/recordings if applicable.
• I’ve included tests if applicable.
• I’ve documented my code using JSDoc format if applicable.
• I’ve applied the right labels on the PR.
• I’ve properly set the pull request status to "ready for review".

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 issue it closes and includes the necessary testing evidence such as recordings and or screenshots.