Adding CSS not working

Hi,

Module installed all seems to be working on the UI front but when I try to add CSS to one of the menu links there is no change.

Basically what I want is one of the menu words the CTA link in a different colour to stand out, nothing too complex.

I am using the main menu and it is using superfish.

I made a new CSS line on my style sheet and added its reference into the attributes bit and nothing.

I am also confused about where I should put it, in style or class?

Thanks