Replace our CSS parsers with an external parser
**Background**: We are doing a bit too much work than we should by writing our own parsers for css property values (e.g. gradient, shadow, background).

**Task**: Research css parsers (e.g. https://github.com/reworkcss/css ), and replace our parsers.


🤔does any CSS parser parses property values?
🤔can we use the native [CSSOM](https://developer.mozilla.org/en-US/docs/Web/API/CSS_Object_Model) instead?