calc parameters containing a + are improperly compressed, breaking browser compatibility

[GreenGremlin]

calc(10% + 5px) is compressed to calc(10%+5px) which is invalid css.

[GreenGremlin]

See the MDN doc on calc:

"Note: The + and - operators must always be surrounded by whitespace."

https://developer.mozilla.org/en-US/docs/Web/CSS/calc