Collect all parameter values from a css property in functional notation

Fix an issue in collecting css property value that misses to collect a parameter if it immediately follows a comma (no whitespaces in between).

For example, when collecting the property value for `background: linear-gradient(to right, rgba(255,255,0), #fff);`,  we missed to collect `255` and `0` from `rgba(255,255,0)`. So the returned array has an entry for `,` and another for `), ` instead of `255,` and `0), `.

@redmunds Can you review this?