Hi VR V,
Please attached screenshot if possible.
You can check CSS class for respective F4 Help and Drop down in IE-11 by Developer Tool(F12).
Kindly render on UI Controls using Developer Tool and Know which CSS class is applied and make change in custom theme.
* Do not change in standard theme Sap Trade Show. It will be infected in all WEBDYNPRO Component
Thanks & Regards
Kishan Rana