bootstrap less => common.less

https://github.com/markdotto/Preboot.less/blob/master/bootstrap.less

.border-radius(@radius: 5px) {
    -moz-border-radius: @radius;
    -webkit-border-radius: @radius;
    border-radius: @radius;
}

.box-shadow(@shadow: 0 1px 3px rgba(0,0,0,.25)) {
    -moz-box-shadow: @shadow;
    -webkit-box-shadow: @shadow;
    box-shadow: @shadow;
}

.opacity(@opacity: 100) {
    -khtml-opacity: @op / 100;
    -moz-opacity: @op / 100;
    filter: e(%("alpha(opacity=%d)", @opacity));
    opacity: @op / 100;
}

.size(@height: 5px, @width: 5px) {
    height: @height;
    width: @width;
}
.square(@size: 5px) {
    .size(@size, @size);
}

.transition(@transition) {
    -moz-transition: @transition;
    -o-transition: @transition;
    -webkit-transition: @transition;
    transition: @transition;
}