How is responsive layout done in 2017?

Question

css

The problem is classic: you need to make the page layout responsive. So far I'm testing on firefox, I will make a separate version for other browsers.
Only two options come to my mind:
1. Make a large (about 90 kb or more) CSS file using media for several resolutions up to 1024x800 inclusive.
2. Use bootstrap and other frameworks.
The second option is no longer needed, because I want to learn how to do it right with my hands first, and then simplify the work (and even then I don’t really like it). I see no reason to implement RESS: a person can be visually impaired and zoom in to 600%.
Therefore, the question is: how do they implement responsive layout today (if you do not take into account bootstrap)
Fixed: cant with a separate version for browsers. Wrote nonsense, figured out the problem. Ordinary cross-browser compatibility solves everything. The rest is adaptive.