How to display product options with the ability to specify the quantity of this option in Opencart 2.x?

Question

opencart

For example, there are 3 sizes - S, M, L, you can specify 3 pieces on the product card. S, 2pcs M. I saw plugins like super options, but there is somehow a lot of things mixed up, I would like to do it without a plugin, tell me where to dig.