Any Media Query for changing size of mobile sidebar within functions.php?

I was looking at “Creating and using a different sidebar” in this:
https://kriesi.at/support/search/?bbp_search=change+the+grid+units+in+the+functions.php+

It gives instructions on how to put this code in functions.php, but I have further questions:

1. Is it the same situation in Enfold in 2020 as it was in 2014?

2. If we only want the widening of the sidebar for mobile, is there any way to indicate that within functions.php code?
if media query is < 767px etc.???

3. I presume CSS is still out of the question? If not, can you tell me what I should try?

Thanks for any direction you can give me.

Seems like a rather popular question.