ttk button background not changing color after theme has been set - python tkinter

I am creating a tkinter GUI using ttk, and I have downloaded and imported the Azure theme for my project. I then tried to change the color of one of the buttons to red using a style but this didn't work despite no errors coming up. The button just remains the default for that theme (it does respond to other options I can specify in the style like padding, so I don't think it's an issue with the style itself.

Here is an example of my problem:

import tkinter as tk
from tkinter import ttk

def myfunc():
    print("Button Clicked")


root = tk.Tk()
root.geometry("200x200")
root.tk.call("source", "C:/Users/samue/OneDrive/Desktop/Website folder/Azure-ttk-theme-main/azure.tcl")
root.tk.call("set_theme", "dark")

buttonstyle = ttk.Style()
buttonstyle.configure("custom.TButton", padding=0, background="red")

mybutton = ttk.Button(root, text="Click Me", command=myfunc, style="custom.TButton")
mybutton.pack()

root.mainloop()

Sorry this is not wholly reproducible, you will have to download the azure theme to run it (and modify the path). Azure can be found here: https://github.com/rdbende/Azure-ttk-theme

Snippet:

from tkinter import ttk
from tkinter import Tk

root = Tk()
style = ttk.Style()
button_1 = ttk.Button(root, text='click me')
style.theme_use('alt')
style.configure('TButton', font=('Helvetica', 14), background='blue', foreground='white')
style.map('TButton', background=[('active', 'green')])
button_1.pack()

root.mainloop()