What do you mean by "your" tbuttons?
If you use LCL's TButton, it is painted by desktop theme, so it should get the same appearance by default.
In my system (Mint 19, Xfce), there is no green border, but a "focus rectangle" inside button. It is quite same in MessageDialog and buttons I put on form.
See attached snapshots.
I have created the buttons (and form) manually, not by dropping objects onto the form designer.