How to make a vertical menu with scrolling on the second and third level?

Question

css

There is a menu with 3 levels of nesting.
If there are more elements on the second level than on the first, then the second level should be scrolled.
And then there should be a srkol of the third level.
When specifying overflow: auto for the second level, there is a scroll, but it cuts off the third level, or scrolls beyond the 3rd level.
It is necessary like this: https://yadi.sk/i/JkftfJ87ntN5_A
how to push the third level, and have scrolling by 2m?

Answer 1

wang, that the third level is a child of the second, try to push it one level up the tree