Theme dropdown not working

i noticed when selecting different theme options (Default, Neon Retro, Dark Mode, Ocean Blue) in the Pong Game, the background or UI does not change. The dropdown is clickable, but no visual change happens.

**Steps to Reproduce:**

1. Open the Pong Game.

2. Go to the Theme dropdown.

3. Select any option other than the default or current.

4. Observe that nothing changes on the game screen.

**Expected Behavior:**

The game UI should update immediately based on the selected theme.
for example: dark mode->background turns black ,paddles and ball turns white and soon.

**Actual Behavior**:

No changes occur when selecting a different theme. The game UI remains the same.

**Environment:**

Browser: (e.g., Chrome / Edge)

OS: Windows 11

**Possible Solution:**

There may be an issue with the theme-switching logic in JavaScript or CSS classes not being applied correctly.