It’s much easier to use nested canvases for this, the idea is similar to a handling a draggable window, more info here:
Otherwise you’ll spend half the time recalculating scrollbox offset position, which is no fun at all. If you want manual handles to shift stuff about, consider sliders - much easier implementation.
The only somewhat difficult concept here is zooming in on the current mouse position as it requires a transform. That’s providing you need that functionality to start with.