Rollover Icons Jquery with Category Icons

Hi, I am trying to have category icons that have a rollover effect , ideally a fade-in, but if I can get any sort of rollover effect, I’ll be happy…

I am trying to use this How-to: https://www.category-icons.com/2008/05/how-to-make-rollovers-with-jquery/, but it doesn’t seem to work for me.

My website is https://www.robotspacebrain.com

I don’t know how to edit this to make it work for me:

jQuery(function($) {
    $(document).ready(function(){
        // Posts
        $("#content h2>img").each(function () {
            rollsrc = $(this).attr("src");
            rollON = rollsrc.replace(/.png$/gi, "_over.png");
            $("<img>").attr("src", rollON);
        });

        $("#content h2>a").mouseover(function () {
            imgsrc = $(this).children("img").attr("src");
            matches = imgsrc.match(/_over/);
            if (!matches) {
                imgsrcON = imgsrc.replace(/.png$/gi, "_over.png");
                $(this).children("img").attr("src", imgsrcON);
            }
        });

        $("#content h2>a").mouseout(function () {
            $(this).children("img").attr("src", imgsrc);
        });

        // Sidebar
        $("li.cat-item>a").mouseover(function () {
            imgsrc = $(this).children("img").attr("src");
            matches = imgsrc.match(/_over/);
            if (!matches) {
                imgsrcON = imgsrc.replace(/.png$/gi, "_over.png");
                $(this).children("img").attr("src", imgsrcON);
            }
        });

        $("li.cat-item>a").mouseout(function () {
            $(this).children("img").attr("src", imgsrc);
        });
    });
});

I also put this in the functions.php:

wp_enqueue_script('jquery');
wp_enqueue_script('caticons-rollover', get_bloginfo('template_directory').
                                       '/rollover.js');

I have been trying to use firebug to see how I can do it, but with no luck, whenever I rollover, the images just disappear and never come back… I have the images in the same folder as the _over.png files as well

Any help would be greatly appreciated! I’m not too great with css/html…