Percentage support

[dwrth]

Proposed solution

Fixes #651 by adding support for percentages.

Tradeoffs

No known ones

Testing Done

Works nicely, also added a new storybook section for this

[bokuweb]

@dwrth

Thanks for your great work.

I think your approach is more rigorous and preferable, but since size is defined with the following interface and writing '50%' is interpreted as a percentage, it may make sense to align the policy with that.

Specifically, how about defining it like position?: { x: (number | string), y: (number | string) };, so that, just like size, writing 50% would enable percentage-based values? That would also keep the design consistent with size.

[dwrth]

@bokuweb I like that idea, makes it much more intuitive when it's aligned like that! Changes have been added