My application looks beautiful on Windows

But on MacOS and Linux it does not look nice at all!

Is there something I can do to help make this widget appearance consistent across operating systems?
My application source code : http://pae.st/BILs/
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Using Tkinter’s
placemanager for widget layout causes the poor layout of your application on different operating systems. You should be using eitherpackorgridmanagers, both of which will adjust to the differing widget sizes you encounter.