Ok, so I've successfully cloned the Elemental theme into applications/themes and I'm wondering how to clone a preset?

I've copied the royal.less file to custom.less in the css/build/fonts folder. I've copied the royal.less to custom.less in the css/presets folder and modified it to reference the custom.less in the fonts folder and changed the preset name.

The preset shows up fine in customize theme, but when I select it, the preset reverts back to whatever it was previously - i.e. my preset won't stick.

What am I missing?

Thanks,
John