I'm having the problem, that I can only use the SharePoint 15 Hive (Program Files\Common Files\Microsoft Shared\Web Server Extensions\15\TEMPLATE\LAYOUTS\1033\STYLES) to save my own themable.css and specify it in the masterpage.html like:
<!--MS:<SharePoint:CssRegistration Name="Themable/themable.css" runat="server" enableCssTheming="true" >--><!--ME:</SharePoint:CssRegistration>-->
I have tried numerous other ways of locating and referring to this file. I already tried the Style Library (Master Page how to specify correct Path for CSS and Images), but maybe because I use theming it also did not work.
Nevertheless, this should not be the preferred way. Additionally, it is very inconvenient for testing, as I must use the server every time and cannot use SharePoint Designer for handling the themable file.
Where must (or can) I locate my themable.css and how to refer to it in the CssRegistration in my master?