Cumulus Support

I'm pretty new to the HTML language and am very happy with the support found in Wiki so far.
I would like to edit my web page with a panoramic photo of my backyard (overwriting the standard header "Altona Forest Weather".
Please give me a hint of how to edit the weatherstyle.css or indexT.html file.
Thanks so much.
I have attached the photo to give an idea of how it should look.

It is a lot easier to help if you provide the link to your existing website. Then we can see what your CSS is etc...