Hello, I’m new here! 
I was wondering why my button doesn’t work when my browser window don’t run in fullscreen. Even if I resize the browser window a bit, the button stop working. 
It would be very helpful to see an example of your code at Playground. Otherwise it is quite hard to guess what is happening on in your case.
If you cannot make a repro in PlayGround, you could just share your code.
Thanks @labris, exactly what I was thinking and otherwise, welcome @Grumpy-Potato, your pseudo rocks !!!