Python - tkinter, ttk, change style

import tkinter as tk
from tkinter import ttk


class Salman:

    def __init__(self):
        self.mainwin = tk.Tk()

        self.label = ttk.Label(self.mainwin, text="simple practice", font="italic")
        self.label.grid(row=0, column=0)

        self.button = ttk.Button(self.mainwin, text="button", command=self.clickme)
        self.button.grid(row=1, column=3)

        self.textvar = tk.StringVar()
        self.entry = ttk.Entry(self.mainwin, width=12, textvariable=self.textvar)
        self.entry.grid(row=1, column=2)

        tk.mainloop()

    def clickme(self):
        self.label.configure(text=self.textvar.get())
        self.button.config(text="ihave been clicked")

        style = ttk.Style()
        style.configure("TButton", foreground="blue")
        style.configure("TLabel", background="yellow")


nomi = Salman()