Improve css util

[owjs3901]

The css uitl can not be used with dynamic variables like this.

css({ w: "100%" }) // OK
css({ w: v }) // Impassible

Because, dynamic variables are applied through the style prop, While the css util works without JSX syntax.

However, you can use the css util with dynamic variables inside jsx..

css({ w: v}) // still not allowed

const a = <Box className={css({w: v})} /> // OK