exact name tags for elements – Tagline – Social Block and nav menu

I am probably phrasing this incorrectly, but I would like to know if there are exact names for the

Tagline – Social Block and nav menu

that are different when on a desktop as opposed to a mobile screen?

The bottom line is I would like to manipulate the

Tagline – Social Block and nav menu

on the desktop while leaving it alone to stay centered on the mobile screen.

I was theorizing that if i knew the exact name tag for each element on the full screen it would leave it alone on the mobile screen.

Unless I am completely confused, which is a possibility, that sort of thing seems to have worked with other css i have played with.

I just can’t seem to figure it out with the

Tagline – Social Block and nav menu