Group administration: Buttons not visible in high contrast mode

Issue Summary

The "close" button are not clearly visible in high contrast mode.

Steps to Reproduce

1. Open the "Group administration" page.
2. Turn ON the high contrast mode.
3. Navigate to the "add user or a group" combo box and activate it.
4. Select users from the list.
5. Observe that the "close" buttons are not visible.

Screenshot

Actual Results

When the user add the user form the list of "Add user or a group" combo box, the "close" button is not clearly visible in high contrast mode.

As a result, low vision user will find difficult to understand the purpose of the button.

Expected Results

The user should able clearly see the buttons present on the page. 

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available.

Environment

MacBook Pro (16-inch, 2021)
macOs Sonoma 14.2
Chrome - Version 120.0.6099.109 (Official Build) (arm64)
Firefox- Version 92.0 (64-bit) 
Safari- Version 17.0 (19616.1.27.211.1)
JAWS- Version 2023
NVDA- Version 2021.2 
Voiceover - Version Latest