hey there. looking at your three png looks like what you need is a custom scorllbar developed with jquery.
that kind of dark scrollbar is something related to a dark theme in the browser. you know, the scrollbar can't be styled with css. so, you need jquery to hide the default one and build a new one.
i can do it for you, and create a custom scrollbar that will match with the colors of your site.
hope we can work together!
regards.