Three circles in one div

index.html

<div></div>

style.sass

div
  margin: 100px auto
  $size: 25px
  position: relative
  
  &:before, &, &:after
    display: block
    height: $size
    width: $size
    border-radius: ($size / 2)
    background-color: red
    content: ''

  &:before, &:after
    position: absolute
      
  &:before
    left: -$size * 2
  
  &:after
    left: $size * 2