Converting PPT Templates to Keynote Themes --- NEED Help

I really like a few of the PPT templates I have, but my district is removing PPT and I would still like to use the themes but in Keynote instead. I opened each PPT template in PPT and saved them out as PNGs. I then opened Keynote and used the PNGs as an Image Fill. I then saved the whole thing as a new theme.

I can see the NEW theme in the theme chooser but when I click on it I get a blank keynote...no theme at all, but the picture of the theme is sitting in the theme chooser. I looked at the files and they are all the correct extension. I tried restarting Keynote, but no change. I am VERY frustrated! Does anyone have any ideas?