Customize scrollbar

Hello,
I was wondering if there is a way to customize the scrollbar in template creator ck.

I explain what i need to do:
I need to have a part of the template (see image attach: the blue list on the left) with a certain height (for example 300 px).
I found a way to do this adding some css in the section "custom CSS". I add this:
#left {
height: 200px;
overflow-x: hidden;
overflow-y: scrolling;
}

Now i need to personalize the "look" of the bar. So i have installed another extension for that, but it only works with the scrollbar of the entire page (see image attach).

Maybe someone have any idea to do this?
Thanks!

Hi
I don't think that this is related to template creator. You shall ask the extension developer that you use to customize your sidebar, and ask him how to manage to customize also something else

how use a technique like this
www.codeproject.com/Tips/674478/Customize-Scrollbars-using-CSS

CEd