Instead of typing


    width:200px; height:200px;

just type


    @include size(200px);


    @include size(20px,35px);

Mixin:

@mixin size($width, $height: $width) {
      width: $width;
      height: $height;
}

HTML:


     <div class="square"></div>


     .square { @include size(200px); }

.square {
  width: 200px;
  height: 200px;
}