Как изменить цвет специальной рамки в Tkinter TTK?

Я хочу изменить фон моей формы ttk (сценарий кода ceasar) на цвет, который у меня есть в моем окне = #FEFB22

Я хочу изменить белый цвет «коробки» на #FEFB22 нажмите, чтобы увидеть изображение!

from tkinter import *
from tkinter import ttk

# variables
letters="ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZ"

# fenetre 
root = Tk()
#window title
root.title('Cesar Crypt/Decrypt par Maxence')
root.iconbitmap("logo.ico")
# allows for window to be resized
root.geometry("850x480")
# window background
root.configure(background='#FEFB22')



root.frame_header = ttk.Frame()



ttk.Label(root.frame_header, text = 'Code César', style = 'Header.TLabel').grid(row = 0, column = 1)
ttk.Label(root.frame_header, text = 'Entrez un nombre entre 1 et 25  :', style = 'Header.TLabel').grid(row = 1, column = 0)
ttk.Label(root.frame_header, text = 'Votre Message:', style = 'Header.TLabel').grid(row = 2, column = 0)
ttk.Label(root.frame_header, text='Votre message crypté/decrypté:',style='Header.TLabel').grid(row=4, column=0)

enc_dec_text = ttk.Entry(root.frame_header, width=110)
enc_dec_text.grid(row=4,column=1)

cipher_shift_menu = StringVar()
Spinbox(root.frame_header,from_=1, to=25, textvariable=cipher_shift_menu).grid(row=1, column=1)


text_entry = ttk.Entry(root.frame_header, width=100)
text_entry.grid(row=2,column=1)

def encrypt_text():
    stringtoencrypt = text_entry.get()
    stringtoencrypt = str(stringtoencrypt)
    stringtoencrypt=stringtoencrypt.upper()
    ciphershift = cipher_shift_menu.get()
    ciphershift=int(ciphershift)
    stringencrypted=""
    for character in stringtoencrypt:
        position = letters.find(character)
        newposition = position+ciphershift
        if character in letters:
            stringencrypted = stringencrypted + letters[newposition]
        else:
            stringencrypted = stringencrypted + character
    enc_dec_text.insert(0, stringencrypted)

def decrypt_text():
    stringtodecrypt = text_entry.get()
    stringtodecrypt = str(stringtodecrypt)
    stringtodecrypt=stringtodecrypt.upper()
    ciphershift = cipher_shift_menu.get()
    ciphershift=int(ciphershift)
    stringdecrypted=""
    for character in stringtodecrypt:
        position = letters.find(character)
        newposition = position-ciphershift
        if character in letters:
            stringdecrypted = stringdecrypted + letters[newposition]
        else:
            stringdecrypted = stringdecrypted + character  
    enc_dec_text.insert(0, stringdecrypted)

#add image
width = 200
lenght = 200
image = PhotoImage(file="logort.png")

#bouton image
button = Button(root, image=image, bg='#FEFB22', bd=0, relief=SUNKEN)
button.pack()

# boutous
encrypt_button = ttk.Button(root.frame_header,text='Encrypter',command = lambda: encrypt_text()).grid(row=3,column=0)
decrypt_button = ttk.Button(root.frame_header,text='Decrypter',command = lambda: decrypt_text()).grid(row=3,column=1)



#bouton q
# uitter
bouton_quitter = Button(root, text="Quitter !", command=root.quit, font=("Courrier", 20), bg='#000000', fg='#FEFB22')
bouton_quitter.pack(side=BOTTOM)

root.frame_header.pack()
root.mainloop()