How to correctly subtract the content scroll step size?

Question

css

Hello, please tell me how to correctly subtract the content scroll step size based on its size?
Or do they calculate differently?
The problem is in the step, either there is a gap, or such as it is now, it scrolls too much.
Thank you.

Example

Answer 1

You don't have to count anything.
It's enough just to hide the scrollbar, for example like this. jsfiddle.net/ufp8hqka/1