`background: rgb(var(--my-var, 0, 0, 0));` parses as valid for both `background-color` and `background-image`

[bryan-codaio]

In react we've got a component that does effectively

<div style={{background: 'rgb(var(--my-var, 0, 0, 0));'}} />

and when we later coerce that to a string per jest snapshot tests, we get back

<div style="background: rgb(var(--my-var, 0, 0, 0)) rgb(var(--my-var, 0, 0, 0));"></div>

Best I can tell this is due to it being parsed as valid for both background-color and background-image per

cssstyle/lib/parsers.js

Line 357 in 11fa40f

if (type === exports.TYPES.NULL_OR_EMPTY_STR || type === exports.TYPES.VAR) {

. I.e. the value in question is being detected as a variable (which isn't completely inaccurate, given its use of var() internally). However, the wrapping rgb should indicate it's not valid for background-image?