Where do I find the item fields CSS?

For what area? There is different CSS for different display areas. The CSS for the Article View Blocks on listing pages is different than the CSS on an item page (which by the way has different CSS for location areas on the item page). You need to be specific.

ie, Sidebar Block for Custom Fields. or custom fields in the header area of the item or fields on the content tabs etc... AMS is even more complex.

 

First thing to keep in mind is that all custom field CSS is first driven by Core XenForo. Its only overriden by showcase in specific situations (which there are several in various sc css templates). Any CSS related to a Showcase ITEM is going to be in the template nflj_showcase_item.css If it is something controlled by core xenforo css, you are either going to have to override that via Extra.css, override it by adding it directly to a showcase specific class or edit it directly, however, editing directly will effect everything that uses that core CSS.

There is no one line of CSS that you can edit/add that will change everything. Each specific area (dozens of them) is very specific for that area.

 

ya, like what TJ mentioned, sometimes class order comes into play and its necessary to use !important to make sure it gets over ridden regardless of order of precedence.