fix: solve css syntax

[preda-bogdan]

Summary

Fixed extra & in CSS syntax.

Will affect the visual aspect of the product

NO

Screenshots

Test instructions

1. On a fresh Neve instance check no W3C Validation errors are shown.

Check before Pull Request is ready:

• [ ] I have written a test and included it in this PR
• [x] I have run all tests and they pass
• [x] The code passes when running the PHP CodeSniffer
• [x] Code meets WordPress Coding Standards for PHP, HTML, CSS and JS
• [x] Security and Sanitization requirements have been followed
• [x] I have assigned a reviewer or two to review this PR (if you're not sure who to assign, we can do this step for you)

Closes #4251.