scss 的 @each指令

 1 $numArray: 10, 20, 30, 40;
 2 @each $propKey, $propVal in (m: margin, p: padding) {
 3     @each $directionKey, $directionVal in (t: top, r: right, b: bottom, l: left) {
 4         @each $num in $numArray {
 5             .#{$propKey}#{$directionKey}-#{$num} {
 6                 #{$propVal}-#{$directionVal}: ($num) + px;
 7             }
 8         }
 9     }
10 }

.mt10 {
    margin-top: 10px;
}
.mt20 {
    margin-top: 20px;
}
...
.ml40 {
        margin-left: 40px;
}
...
.pl40 {
    padding-left: 40px;
}