I have a var like this:
--size-sm: 15px;
And want to use it for a negative margin.
        a:first-child {
          margin-left: var(--size-sm);
        }
Is there any way how the value could be inverted? I tried few syntax like margin-left: -var(--size-sm); and margin-left: -(--size-sm); without success. 
 
    