New user needs advice on Additional CSS

Hi all

I’ve recently registered as non-business user with dreamhost and am setting up a site based on a template.

I would like to change the font and the only way I can see to do this is via CSS as there are not font options anywhere that I can see.

I have tried editing the css sheet, I have tried using the Additional CSS on the customize page but neither results in a change in font. Am I missing something on the formating perhaps? I’ve looked around for help but while css help in general is easy to find, if it’s not having an effect I must be doing something wrong.

Is there a help page to outline how to use the Additional CSS box? Is there something obvious I’m overlooking?

FWIW I’m using the Argent theme - I like its very plain and simple look but the font used for the header looks completely out of place.

Edited to add - I realised I could add plug-ins to do this, so have managed to change the font. Still not sure what I’m doing wrong in the additional CSS box though.