Correct implementation of mobile first?

Question

css

Good afternoon.
I read about mobile first, etc., but I didn’t read one anywhere (or maybe I’m just not attentive).
When laying out using the mobile first method, is it first laid out for mobile devices, and then for other widths? Or first for desktop => tablet => mobiles ?

Answer 1

it is necessary to typeset for two or three sizes at once, using
mobile-first media queries - this means that this is the main paramount platform the
code must be universal - it works equally on both mobile and desktop