Consider non-grouped styles as base #29

In Stitches, we put "base" styles in the object like so

const RedBox = styled('div', {
 backgroundColor: '$red'
})

In macaron, following vanilla-extract, we use the base keyword

const RedBox = styled('div', {
 base: {
 backgroundColor: '$red'
 }
})

I'm not sure what the benefit of using base is here, perhaps there is some good reason but could we possibly support both syntaxes? It would surely make it just a little easier for our team to migrate from stitches to macaron.