@AkshayS94559312 

It comes from CSS Includes. You can inspect and find the class name and then find it in css includes.

1. Navigate to sp_css.LIST
2. Filter with css contains "select2-highlighted". Most probably this will be the class name.
3. Open the relevant record and find out where select2-highlighted is defined and set it accordingly.

If you have found a different class name in inspect then find the same in sp_css table.

Accept the solution and mark as helpful if it does, to benefit future readers.
Regards,
Sumanth