Support dark and light adaptive props

[argyleink]

fixes #11

todo:

• add documentation

[PapiPeppers]

Is it possible to place the dark mode props under a specific class or attribute selector, instead of placing them into a media query? I have a theme toggle that updates a root data-attribute and class upon a toggle change event so placing the css variables into a prefers-color-scheme media query won't work.

I'm wondering if an option could be added to the plugin to specify where the props get placed (default: media query, custom: [data-attr, #id, .class, etc]), similar to the option to insert the props into a specified layer. The current -@media:dark syntax could be maintained if the plugin created the specified selectors instead of outputting props under the root selector in a media query.

[argyleink]

this is a very meaningful feature request! logged the feature request here #44