enhance dark mode text contrast

[ruiarii]

Description

I changed the $body-emphasis-color-dark variable to $white, it will make the dark mode text appear white instead of the default $gray-500 so there is a better contrast in the text appearance when dark mode is enabled

Motivation & Context

This will improve the contrast between the text and the background, making it easier to read.

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would change existing functionality)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

Live previews

• https://deploy-preview-38530--twbs-bootstrap.netlify.app/

Related issues

#38525

[mdo]

We'll be holding off on making this kind of change for now.