Site-Wide Background Changes

What is the easiest way to change the Site-wide Background color, or background image of certain site builder areas?
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Can this be done via ACP or do we need FTP?
If we need to use FTP where is the global CSS file?
updated by @softdesigns: 11/07/18 08:49:43PM

site wide background color I would look for the current one being used in the CSS at the highest level then either add some extra newer CSS after that one is implements so that your one works, or change it where it is if its in a skin .css file and the skin has been cloned.

Each site builder section will have its own uniquie ID, use that to target it via CSS.

--edit--
It MAY be possible to change the background color via the STYLE tab of the skin, depends if the skin has been setup to allow that as an option or not. ( I prefer the SFTP upload system way of doing things as I find it easier to locate changes later on.)

The skins CSS files will be found at /skins/ YOUR SKIN /css/*

and if you want to add a new css file, add the file there then link to it from inside the skins include.php file in the _init() function. you'll see other examples of how to in there.
updated by @michael: 08/06/18 09:03:00PM