Make it easier to export spinner and loading button to design tool (sketch)

[coderitual]

Currently our spinner is created entirely in CSS (using border-radius technique). This is completely fine and performant solution. It has a flaw though in the context of brainly process. It makes exporting component from code to design tool particular hard task. We would need to implement special converter to handle this kind of css visuals (and I would say it would be really difficult considering you can create basically any image in css).

Proposed solution is to use SVG to represent spinner element.