Why my jQuery for the #NextButton does not work?

Hi all,
I tried to implement an onclick function for the next button in a survey which was designed using the old Look&feel editor (theme: Minimal - blue).
MWE: `jQuery( "#NextButton" ).click(function() {alert("OK");});`

I tried to solve this and wasn't succesful, but I found out following:

1. Other codes using this jQuery also doesn't work (e.g.: `jQuery(".NextButton").css("background-color", "yellow!important");` or `jQuery(".NextButton").hide();`)
2. Using the classname instead of the ID didn't help.
3. ID and class names were correct for actual survey. (I've checked this using inspector)
4. There are no errors in the console log (in both Mozilla and Chromium).
5. jQuery for other elements

Would anyone have some suggestions what else could I check or try? I'd appreciate also some other ways how to create a function which will run after clicking on the next button.
Thanks for any suggestions!