from tkinter import *
def limpar():
    preco_entrada.delete(0, END)
def app():
    p = preco.get()
    d = p*0.06
    pf = p-d
    pfarr = round(pf,2)
    mensagem = f'{pfarr} €'
    resultado.set(mensagem)
root = Tk()
root.geometry("400x250")
root.resizable(0, 0)
root.config(bg="#d9ead3")
root.title("Redução de 6% para 0% de IVA")
titulo = Label(text="Redução de 6% para 0% IVA",
               font=("Arial", "15", "bold"),bg="#d9ead3",fg="#bf9000")
titulo.place(relx=0.15, rely=0.05)

texto_sub1  = Label(text="Preço com 6% de IVA:",
                    font=("Arial", "12", "bold"),bg="#d9ead3",fg="#bf9000")
texto_sub1.place(relx=0.1, rely=0.35)
preco = DoubleVar()
preco_entrada = Entry(textvariable=preco,
                             font=("Arial", "12", "bold"),
                             bg="white", fg="blue", justify='center')
preco_entrada.place(relx=0.55, rely=0.35, relwidth=0.3)
#
but1 = Button(text="Ver", bd=2, bg='#107db2', fg='white',
              font=('verdana', 12, 'bold'), command=app)
but1.place(relx=0.15, rely=0.55, relwidth=0.25, relheight=0.1)
but_limpar = Button(text="Limpar", bd=2, bg='#107db2', fg='white',
                    font=('verdana', 12, 'bold'), command=limpar)
but_limpar.place(relx=0.55, rely=0.55, relwidth=0.25, relheight=0.1)

texto_sub2 = Label(text="Preço sem IVA: ",
                           font=("Arial", 12, "bold"), bg="#cfe2f3")
texto_sub2.place(relx=0.1, rely=0.75, relwidth=0.35,relheight=0.2)

resultado = StringVar()
resultado_texto = Label(textvariable=resultado,
                           font=("Arial", 12, "bold"), bg="#cfe2f3")
resultado_texto.place(relx=0.5, rely=0.75, relwidth=0.35,relheight=0.2)
root.mainloop()