I have created an extension to make a specific web site easier to use. So I do not have access to the source code. I only want to modify the CSS; I am not asking how to hack the web site. This is not worth a lot of effort so there is no need to spend much time on this.
The web site apparently uses Vuebar; a fiddle showing sample use of that is at Vue 2.0 Hello World - JSFiddle. Note that in that sample, there is a scroll bar (something like a scroll bar) at the right of the sample. Note that we can scroll using the mouse wheel and we can scroll by dragging the scroll bar but we cannot (I cannot) scroll by clicking in the scroll bar, like we can in normal scroll bars.
Is there an easy modification of the CSS to allow scrolling by clicking with the mouse like for normal scroll bars? If it is not easy then I won’t bother pursuing this. If I had developed the web site then I would not use a custom scroll bar like that. I could write a lot of code to replace the custom scroll bar with a regular scroll bar but this is not worth it.