Why can not I change collider`s border manually? I remember being able to do that. I just clicked the gray button under in this case Box Collider 2D component, then went to the Scene view and tweaked it as I wanted by clicking and moving collider`s border. But now when I do the same procedure on trying to click and drag the border in Scene view I am just losing focus of the collider, but do not change it in any way.
You need to reset layout to
Default and then back to your work layout (if needed) and collider editing will work.
Also, you can close the
Hierarchy tab and then - reopen it.