I find it hopeless to achieve anything with applications aimed at non-devs, such as PowerPoint. How the hell can it be so difficult to use the same theme in one presentation as in another? If it had been code, I would just have copied the XML, XAML, include, link, script or whatever code in whatever language on whatever platform from the old project and pasted it into my new project. But with "user-friendly" apps I have no control of how anything actually works. I give up, my presentation will be unthemed. Maybe it's for the better anyway, less distracting graphics.