Thread:Project:Support desk/Custom tables with css/reply

No need to change the core files at all.

Edit on your wiki and add something like

Depending on what styles you want it to have you may find the build-in  good enough:

It does mean you have to use "class=wikitable" everywhere but I think that's worth it since in some cases you may want to use tables without this styling. (eg. for infoboxes)