Board Thread:Support Requests - Getting Technical/@comment-28470696-20171205002426/@comment-9605025-20171205015552

CSS and HTML are meant to work together. There is no such thing as a pure CSS site or a pure HTML site. Putting CSS in HTML tags is not a "Fandom thing", it is called inline styling and it is part of official HTML specifications.

The example you have given uses purely inline styling. Due to the markup interpreter (which is a "Fandom thing" since it needs to handle both MediaWiki markup and Fandom's custom tags), you cannot specify a background image using inline styling (note that there are also limits on the HTML tags you can use). However, as Fngplg was trying to say, it can be done using site-wide (i.e. stylesheet) CSS. You can make stylesheets the same way you make any other page on your wiki; just be sure the page name ends in ".css". Note, however, that only a few pre-named stylesheets are actually loaded. For more information on these pre-named stylesheets, see Help:Community_CSS_and_JS, Help:Advanced_CSS_and_JS and Help:Personal_CSS_and_JS.

You can use additional stylesheets through use of @import. For example, I have created my own stylesheet to fix some display issues in Internet Explorer 11 (here). I then include it in my global (personal) CSS. As such, that CSS is applied when I view any Wikia site.