ttk.Progressbar does not change the Layout
You don't need to create a new element if you only want to change its options, in your case just configure the "Niklas.Horizontal.TProgressbar" style:
import tkinterfrom tkinter import ttkmaster = tkinter.Tk()s = ttk.Style()s.configure("Niklas.Horizontal.TProgressbar", troughcolor="#121212", background="#b2b2b2", thickness=1, troughrelief="flat", relief="flat", borderwidth=0)pb = ttk.Progressbar(master, style="Niklas.Horizontal.TProgressbar", orient="horizontal", mode="determinate", maximum=230)pb.grid(columnspan=2, sticky='ew')pb.start()master.mainloop()An issue I identified in your code is that you gave the progressbar the style "Niklas.Horizontal.TProgressbar.trough", which is not a progressbar style but an element of the style, so the progressbar did not work.