Hi! Gravity form – edit i javaskrip, how?

First of all, I LIKE this plugin, and have used it for over 2 years as a way to add Google Translate script to various themes I have used. What I never really felt comfortable with was the attached (?) jQuery scripts that I always wondered if they were just adding unneeded overhead to my site if I didn’t use any of them (I never did). Recently, I’ve been trying other plugins designed to add JS to my site WITHOUT any extra code. It’s a hard thing to find. Popular competitors such as: CSS & Javascript Toolbox , and Custom css-js-php offer additional options BESIDES just adding JS.

Currently I’ve uninstalled this plugin, and decided to try out the Custom css-js-php Plugin instead. If any Automattic developers see this post, do you think I have made a mistake, or have any comments on my decision ?

https://www.ads-software.com/plugins/custom-javascript-editor/

Okay here I stand. I have installed and activated the plugin into my site and I need to execute the following function in it.

$(window).scroll(function() {
    $(this).scrollTop() > 0 ? $('body').css('background', '#f0f') : $('body').css('background', '#0f0');
}).scroll();

NB: The function is related to header image of my site

I tried to copy and paste the function in the plugin. But the plugin tends to show me errors which are not understood by me.

Do I need to define functions somewhere in my website *.php files?
If yes then where and how should I define it?

Please provide detailed answer.
Thanks in advance

https://www.ads-software.com/plugins/custom-javascript-editor/

Print Screen: https://i.imgur.com/BQxeK.png

https://www.ads-software.com/extend/plugins/custom-javascript-editor/