The Less compilers that I\'m using (OrangeBits and dotless 1.3.0.5) are aggressively translating
body { width: calc(100% - 250px - 1.5em); }
There is several escaping options with same result:
body { width: ~"calc(100% - 250px - 1.5em)"; } body { width: calc(~"100% - 250px - 1.5em"); } body { width: calc(100% ~"-" 250px ~"-" 1.5em); }