Update submenu and overlay color of the header navigation

[carolinan]

Description

This PR adjusts the submenu and overlay text and background colors for the navigation block in the header patterns.
Note that I did not update other patterns like the footers, because they have the overlay turned off by default.

Closes #533

Screenshots
I only recorded the default header. After:

default-header-new-colors.mp4

Testing Instructions

Preview all the headers in the theme and confirm that:
The submenu in the navigation block does not have a white background color (unless white is part of the palette).
The overlay or "mobile menu" does not have white background (unless white is part of the palette).

1. Add a few menu items to the main navigation block, including a submenu.
2. Go to Appearance > Editor and select any template to edit.
3. Click on the "View" icon and select mobile.
4. Click on the menu button on the navigation block to enable the mobile menu.
5. Now open the Styles sidebar.
6. Open "Browse styles" and test the different style variations.
7. Change the header template part, and repeat.

[github-actions]

Preview changes

You can preview these changes by following the link below:

• Preview changes for twentytwentyfive

I will update this comment with the latest preview links as you push more changes to this PR.
⚠️ Note: The preview sites are created using WordPress Playground. You can add content, edit settings, and test the themes as you would on a real site, but please note that changes are not saved between sessions.

[juanfra]

Thank you. Looks good to me.

Screen.Recording.2024-10-09.at.14.50.51.mov

[github-actions]

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Co-authored-by: carolinan <[email protected]>
Co-authored-by: juanfra <[email protected]>
Co-authored-by: beafialho <[email protected]>

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