updated border to render mobile buttons correctly

[danielfmiranda]

Closes #7195

Link to sample test page: https://foundation-s-7195-mobil-wqnmrs.herokuapp.com/en/

Steps to test:

1. Visit https://foundation-s-7195-mobil-wqnmrs.herokuapp.com/en/
2. Resize the window to mobile width
3. Click the menu icon in the top left of the page
4. The links that then appear underneath, should have a white border on the bottom if active or hovered over. The rest of them should just be white text.

5. If the links appear correctly, testing is done!

Checklist

Changes in Models:

• Are my changes backward-compatible

[github-actions]

This PR introduces visual differences. Click here to inspect the diffs.

[fessehaye]

Looks good 👍

[nancyt1]

Links looks good!