The "Edit CSS" feature isn't working in TikiWiki 2.*, as far as I know. Stylesheets should be edited locally and transfered or copied to the server.
Normally when the stylesheet is edited and uploaded, the changes appear with the next page refresh. If the edits don't show up, it might be necessary to flush the site caches (tiki-admin_system.php), but usually this isn't the case for CSS file changes.