New UI darkmode dropdown is displayed wrong on firefox

Summary

When using the new UI with darkmode (beta) the dropdown-toggle, when opened, displays the X and Y scrollbars and a wrong-looking white gradient

Steps to reproduce

  1. Use latest version with new UI
  2. switch to darkmode
  3. goto any project > build > pipelines
  4. click on "Show Pipeline ID" dropdown button

What is the current bug behavior?

it shows these scrollbars and white gradient overlay

Screenshot_2023-06-28_123611

What is the expected correct behavior?

don't show them

Results of GitLab environment info

We have a self-hosted instance of gitlab GitLab Enterprise Edition v16.1.0-ee