Unity UI How to write user customizable UI?

I have a scroll view of a text mesh pro UGUI display game log, want it to be shrinkable and expandable, or the user could adjust the size of the scroll view. Any idea how to write that? Thanks!

 

Not sure if there is UI out of box solution.
But I know, the one feasible solution is using embedded browser, and make UI in HTML5, or atleast in js.

 

Using embedded Browser feels too complicated and overkill for a small feature.
Feels like there could be a solution using native UI and code control, detect mouse on certain area of the UI and use mouse drag event to change the width or height of the UI.

 

I suppose, you can use canvas and panels.
Just record current mouse position on 2D plane of camera.
For example you can make invisible button, as large, as each UI panel.
Then scale panel, accordingly, to mouse movement, when mouse button is held.