Tkinter - How can I change the default Notebook border color?

[Larz60+]

I found this theme on web, modified for better effect (reference in script):
Credit: project: JAVER_Assist Author: tywings File: main_gui.py License: MIT License
(you can change margin size to see background color (your selection) better.
Colors are from w3schools color picker here: https://www.w3schools.com/colors/colors_picker.asp

from tkinter import *
from tkinter import ttk
 
root = Tk()
root.geometry("400x300")
root.title("Notebook with theme style")
 
# style=ttk.Style()
# style.configure("TNotebook", highlightbackground="#848a98") # if I use another option like - background="#848a98" - the style changes, but with - highlightbackground="#848a98" - option the style doesn't change..

# Origin (modified) of style code: https://www.programcreek.com/python/example/104109/tkinter.ttk.Notebook Number 25

style = ttk.Style()

style.theme_create('pastel', settings={
    ".": {
        "configure": {
            "background": '#ffffcc', # All except tabs
            "font": 'red'
        }
    },
    "TNotebook": {
        "configure": {
            "background":'#848a98', # Your margin color
            "tabmargins": [2, 5, 0, 0], # margins: left, top, right, separator
        }
    },
    "TNotebook.Tab": {
        "configure": {
            "background": '#d9ffcc', # tab color when not selected
            "padding": [10, 2], # [space between text and horizontal tab-button border, space between text and vertical tab_button border]
            "font":"white"
        },
        "map": {
            "background": [("selected", '#ccffff')], # Tab color when selected
            "expand": [("selected", [1, 1, 1, 0])] # text margins
        }
    }
})

style.theme_use('pastel')

MainNotebook = ttk.Notebook(root)
# MainNotebook.place(x=16, y=16)
MainNotebook.pack(fill=BOTH, expand=True)
 
Frame1=Frame(MainNotebook, background="#ffffff", width=200, height=150)
Frame1.pack()     
Frame2=Frame(MainNotebook, background="#ffffff", width=200, height=150)
Frame2.pack()
 
MainNotebook.add(Frame1, text="Tab1")
MainNotebook.add(Frame2, text="Tab2")
 
root.mainloop()

image: