Need Some Help with a Banner

[quasimana]

Hey dudes, 

So I'm sure this is really easy to do, but I have absolutely no idea what I'm doing. I'd like to stick an image at the top of my forum's home page to serve as a banner. Whatever text I stick in my forum's "Main Header" appears exactly where I'd like this image to go, so I imagine I can just the image's URL with proper coding, but beyond that I'm lost. Ideally I'd be able to make this banner image scale to the size of the browser or something, so as not to stretch the page out on tablets or small monitors. If anyone could just teach me how to go about this, that'd be da bomb. 

Forum: omniscientbovine.proboards.com

Thanks in advance!

[quasimana]

Cancal that, chums! Figured it out by sticking this in my CSS:

img {
max-width: 100%;
}

And this in my main header:

<img src="..." />

Sorry for the preemptive post!