HTML page question

Hello!
I find free HTML template for html pages. I downloaded it and there is file "index" where is the HTML code. The second file is "CSS". Where I must put it? Because now my homepage looks like this:

I don't know how to install it. If you want, I will give you the template because it is free.
Thanks!

the CSS goes in the custom css in admin

Since it is downloaded the CSS will likely conflict with a lot of your forums current CSS... so i'd recommend NOT putting it in the CSS in the Admin Panel.

And instead learning a bit about CSS so you know what the issue is and sort it.

Thanks guys i found the code. If someone don't know it :

Spoiler:

Thanks a lot! Now my homepage is super. Lock!