Background color expands outside select component after selection

When an element in a select component is selected the background color of the component is set to gray to indicate that it is in focus. However, the :focus selector rule for the component sets the border radius to 0 which results in a gray background that expands outside the select component itself if a border radius is more than zero. See attachment.

I have searched the theme settings and the component settings, but I have not found a way to fix this issue.

Does anyone know how to fix this?