Looking at Minecraft's widgets for scrolling list, I've found ExtendedList which extends AbstractList. The latter of which handles all the logic for scrolling, etc.

I looked into AbstractList and discovered that render renders the dirt background as well, which I don't want. I only want the ability to scroll, scroll bar and hiding other content that is out-of-view.

With this, will I have to make my own widget for scrolling list? If not, then what other alternatives are there provided by Forge or Minecraft that I've not found?

I already answered it in another post.

In your ExtendedList constructor, call the correct method here:
(link)

Quote

There is a method that allows you to get rid of it:
func_244606_c(false)

func_244606_c(false) // Disables dirt outline
func_244605_b(false) // Disables black background

Note that false disables them, whilst true enables them.