Based on this answer on how to customise the Notebook's Tab's configuration, you can append the font's info into the created theme like so to get the type of fonts you want:
import tkinter as tk
from tkinter import ttk
root = tk.Tk()
s = ttk.Style()
s.theme_create( "MyStyle", parent="alt", settings={
"TNotebook": {"configure": {"tabmargins": [2, 5, 2, 0] } },
"TNotebook.Tab": {"configure": {"padding": [100, 10],
"font" : ('URW Gothic L', '11', 'bold')},}})
s.theme_use("MyStyle")
notebook = ttk.Notebook(root)
f1 = tk.Frame(notebook, bg='red', width=200, height=200)
f2 = tk.Frame(notebook, bg='blue', width=200, height=200)
notebook.add(f1, text="frame 1" )
notebook.add(f2, text="frame 2 longer" )
notebook.grid(row=0, column=0, sticky="nw")
root.mainloop()
The other approach is to directly configure the Notebook's Tab style. See below code.
import tkinter as tk
from tkinter import ttk
root = tk.Tk()
s = ttk.Style()
s.configure('TNotebook.Tab', font=('URW Gothic L','11','bold') )
notebook = ttk.Notebook(root)
f1 = tk.Frame(notebook, bg='red', width=200, height=200)
f2 = tk.Frame(notebook, bg='blue', width=200, height=200)
notebook.add(f1, text="frame 1" )
notebook.add(f2, text="frame 2 longer" )
notebook.grid(row=0, column=0, sticky="nw")
root.mainloop()
You have to note a difference between using
s.configure('TNotebook.Tab', font=('URW Gothic L','11','bold') )
and
s.configure('TNotebook', font=('URW Gothic L','11','bold') )
. The former changes the Notebook's Tab widget's font while the latter changes the Notebook's font.
You use the first approach if you are configuring many aspects of the Tab. You use the 2nd approach if you just want to change the Notebook Tab's font.
Using s.configure('.', font=('URW Gothic L','11','bold') )
means all ttk widgets font will be of the same type. Do this if this is what you want.