What exactly do I put in Wikia.css to change the text of the toggle link from expand/collapse to show/hide?
I believe you are looking for the "data-expandtext" and "data-collapsetext" attributes. There's a section at Help:Collapsing#Custom_wording that has an example of this.
I saw that, but I don't want to use inline stuff on every collapsible table.
What exactly do I put in here to change it to "Show-Hide" on all collapsible tables:
I am not good with CSS stylesheets.
What do you think?