All boxes below should be 100px * 100px and green.

control => PASS
50px + 50px => PASS
150px - 50px => PASS
50px + 50px (2 spaces around operator) => PASS
150px - 50px (2 spaces around operator) => PASS
50px*2 => PASS
50px *2 => PASS
50px* 2 => PASS
200px/2 => PASS
200px /2 => PASS
200px/ 2 => PASS
50px*(2) => PASS
50px *(2) => PASS
50px* (2) => PASS
50px*(1 + 1) => PASS
50px*(12 - 10) => PASS
50px*(10 / 5) => PASS
10px* (5 * 2) => PASS
50px + 10px * 5 (operation order) => PASS
100%/2 (where 100% is 200px) => PASS
100% + -100px (where 100% is 200px) => PASS
80% - 60px (where 100% is 200px) => PASS
300px - 100% (where 100% is 200px) => PASS
-100px + 100% (where 100% is 200px) => PASS
20% + 30% (where 100% is 200px) => PASS
80% - 30% (where 100% is 200px) => PASS
10% * 5 (where 100% is 200px) => PASS
5 * 10% (where 100% is 200px) => PASS
(100px) => PASS
(50px + 50px) => PASS
(50px) + 50px => PASS
50px + (50px) => PASS
50px + 50px => PASS
50px + 25px * 2 => PASS
(25px + 25px) * 2 => PASS
2 * 50px => PASS
2 * 100px / 2 => PASS
(1em - 1em) + 100px => PASS
50px + +50px => PASS
-50px + 150px => PASS
-50px - -150px => PASS
(((((((100px))))))) => PASS
100px => PASS
100% * 2 => PASS