How to fix this css to display menu horizontal?

How to fix this css to display menu horizontal?
0

Hi guys,
I’m following a course of developing wordpress theme,
at some point was to implement a code in the main.css file to display the top-menu bar in horizontal, but did not happen, the list of pages still showing in vertical,
please check the attached screenshots, and see where is the error or missing in this? thanks in advance!