Calc mixin for Sass

calc() mixin

@mixin calc($property, $expression) { 
  #{$property}: -moz-calc(#{$expression}); 
  #{$property}: -o-calc(#{$expression}); 
  #{$property}: -webkit-calc(#{$expression}); 
  #{$property}: calc(#{$expression}); 
}

.test {
@include calc(width, "25% - 1em");
}