Why do the buttons in my window look old in C++?

c++ windows button styles

Postmessage and WS_BORDER

Issue might be that you use WinAPI directly.
Have you tried sending WS_BORDER with PostMessage to the Control and set it 0 ?

c++ windows button styles

Link your manfifest to your application which specifies v6 common controls.http://msdn.microsoft.com/en-us/library/windows/desktop/bb773175(v=vs.85).aspx