// Mixins
=has($element)
  @at-root #{&}__#{$element}
    @content

=variant($modifier)
  @at-root #{&}--#{$modifier}
    @content

// Example
.Alert 
  padding: 20px
  position: relative
  width: 500px
  
  +variant(danger) 
    background-color: #c00
    color: #300
  

  +has(close-button) 
    display: inline-block
    position: absolute
    right: 20px
    top: 20px
    
    +variant(danger) 
      color: #c00;