Arduino LED strip doesn't turn off completely

Problem not solved.

The page you linked to suggests this code:

int brightness = 255;
...
void TurnOff() {
   for (int i = 0; i < 256; i++) {
       analogWrite(GREEN_LED, brightness);
       analogWrite(RED_LED, brightness);
       analogWrite(BLUE_LED, brightness);
 
       brightness -= 1;
       delay(fadeSpeed);
   }
}

Guess what happens if you take 255 and subtract 1 from it 256 times over?

So the problem is still there, on that page. Other beginners will find the same problem and they too will come here asking for help.

@renatompereira If you truly wish to thank is, please contact Ian on that page and ask him to fix his page.