I got an issue with CSS on your div.
Using your plugin to create a CSS-only loading spinner.
I'm pretty sure my CSS isn't the issue (I'll post it too though).
I'm importing the CSS with McKack 's CSS Importer.
Here is my setup and the result.
Div plugin properties:
Nothing else in the event sheet than importing the CSS.
Nothing else in the layout than the div and a background.
Result exported to Firefox or NW.js:
Any way to remove the jiggling?
EDIT: figured it probably has something to do with the rotation keyframes.
Tried out width keyframes, didn't have any jiggling.
Still, I'd love to get rotating to work..