mobile z-index

Problem/Motivation

Can't seem to adjust the z-index on the gin mobile vertical dropdown menu to overlay the webpage header.
Tried setting the z-index higher than the header with no luck. How do you fix it please? See attached screenshot.
Thanks

Drupal 10, Gin 8.x-3.0

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes