Rendering issue

I'm trying to run this simple example code to render a button. When I run the program, I see GUI like this

Could someone shed light on what is causing this issue?

System Information
NAME="Red Hat Enterprise Linux Server"
VERSION="7.9 (Maipo)"
ID="rhel"
ID_LIKE="fedora"
Kernel version- 3.10.0-1160.81.1.el7.x86_64

echo $XDG_CURRENT_DESKTOP= GNOME

**Code **
import tkinter
import customtkinter

customtkinter.set_appearance_mode("System") # Modes: system (default), light, dark
customtkinter.set_default_color_theme("blue") # Themes: blue (default), dark-blue, green

app = customtkinter.CTk() # create CTk window like you do with the Tk window
app.geometry("400x240")

def button_function():
print("button pressed")

button = customtkinter.CTkButton(master=app, text="CTkButton", command=button_function)
button.place(relx=0.5, rely=0.5, anchor=tkinter.CENTER)

app.mainloop()

Start by reproducing the provided CustomTkinter button example on Red Hat Enterprise Linux 7.9 with GNOME, then compare the result with the attached screenshot. Trace the rendering behavior involved in the example and determine a reproducible cause; done means the cause is identified and a fix or actionable resolution is documented.