I'm trying to set a custom logo...
But all I get is this...
First, you need to upload the images. Secondly, you don't change the logo in the CSS - you change it in the theme's options.
ACP >> Templates & Style >> Themes >> Apart Flame
Change the "board logo" value with the URL.
Check if you are adding correct syntax for URL like;
url(URL_OF_YOUR_IMAGE);
There should be ; at the end of )