XF 1.4 Noob questions - Fixed!!

Sorry, very basic question.
I have my image files for header, etc on a separate branch of my website server (same server) and want to keep them there. How do I reference them, please?

My Xenforo is installed on -
And according to the style properties, the current default images are on -
(so they are on - <website>/forum/styles/default/xenforo/)

What do I need to enter instead of <styles/default/xenforo/> if I want to access them on -

I know writing the full URL works, but that seems inefficient - any other way to do it?