Where are the CSS styles stored, which I've created using the drag and drop interface under the tab 'Style'?
Also, where are the CSS styles stored which I've manually added to the 'Advanced' tab under 'Custom CSS style'?
both the CSS codes, the one generated by drag and drop and the one in Advanced tab, are stored in the database in the table #__kiolezo_layouts. The CSS code is retrieved from the database from the component when is needed.
So you can't find them by FTP client.
Besides with the full version of Kiolezo, you can (optionally) export a stand-alone template. In that case, as the template is a normal template, you can find the CSS files into the template folder.