Border around multiple div as one

style.scss

/* http://codepen.io/Ghetolay/pen/PNLKpO */
.container{
  position: relative;
  z-index: 0;
}

$borderSize: 2px;
/* 1px bigger only needed when sizes are float */
$coverBorderSize: $borderSize + 1px;
$bgColor: #f1f1f1;
.element{
  position: relative; 
  background: $bgColor;
  outline: $borderSize solid red;
  
  padding: $coverBorderSize;
  
  &:before{
    content: '';
    position: absolute;
    z-index: 1;
    top: 0;
    left: 0;
    bottom: 0;
    right: 0;
    
    border: $coverBorderSize solid $bgColor;
  }
}