imagine.css

position(
    - justification [left, h-center, right], // - could delimit optional, + could delimit required
    - alignment [top, v-center, bottom]
) {
    // map enum to expressions
    :: [left, top] flex-start
    :: [h-center, v-center] center
    :: [right, bottom] flex-end

    // no colons or semicolons
    display flex
    [justify-content justification] // [] delimits optional
    [align-items alignment]
}

left()     { position(left)     } // () distinguishes function from element
h-center() { position(h-center) }
right()    { position(right)    }
top()      { position(top)      }
v-center() { position(v-center) }
bottom()   { position(bottom)   }

center() {
    h-center // () unneeded if no arguments
    v-center
}

.h1 {
    headline
    center
    highlight
}

.h2 {
    headline
    center
    highlight--alternate // BEM identifiers!
}