duh: default or portal?

New to DNN, want to use the CSS editor. Working on project with another nub like myself, so can someone enlighten me as to which skin.css file is the one in use - Default or Portal?? (Oh, and also the *.ascx file.)  I've heard conflicting information. I have the CSS editor installed in both Default and Portal skins (same skin)  just in case, for now. Thanks.

When you assign the skin in Admin > Site Settings, or on the Page Settings it depends on if you have selected "Host" or "Site".
If you select a skin from "Host" then it is the _default/skins folder, if you select a skin from "Site" then it is the portals/pn/skins folder where pn = portal number.

Muchas gracias! Really appreciate the free editor, as well. Am grateful, in general, for the generosity of the DNN community at large. Couldn't do it without all those who've gone before who share their knowledge and tools.