I believe you can try this and see if does what you are looking for;
Click the start orb and type
advanced system settings
and hit enter
In the top frame labeled Performance, click the Settings button
Uncheck the box that says Show shadows under windows
OK your way back out of there and see if that does the trick.
It is difficult to break out a single component of the Overall Aero / Glass theme effect, but if that doesn't do what you want, then unchecking the bottom box labeled Use visual styles on windows and buttons definitely will.
Regards
Randy