Generated by SassMeister.com.

SassMeister-input-HTML.html

<div class="tester"></div>
<div class="tester2"></div>
<div class="tester3"></div>

SassMeister-input.scss

// ----
// Sass (v3.2.19)
// Compass (v0.12.6)
// ----

@mixin border($color: #000, $width: 1 1 1 1, $style: solid){
  border-color: $color;
  border-style: $style;
  $total: 0;
  @each $side in $width{
      $total: $side+$total;
  }
  @if $total/4 != nth($width, 1) {
    $trbl: top right bottom left;
    @for $i from 1 through length($width){
      border-#{nth($trbl, $i)}-width: #{nth($width, $i)}px;
    }
  } @else {
    border-width: #{nth($width, 1)}px;
  }
}

div{
  width: 100px;
  height: 100px;
  margin: 0 auto;
  background-color: #c2c2c2;
  @include border();
  & + div{ margin-top: 10px; }
}
.tester2{ @include border(#d00,1 2 3 4) }
.tester3{ @include border(#0d0, 5 6 1 2, inset) }

SassMeister-output.css

div {
  width: 100px;
  height: 100px;
  margin: 0 auto;
  background-color: #c2c2c2;
  border-color: black;
  border-style: solid;
  border-width: 1px;
}
div + div {
  margin-top: 10px;
}

.tester2 {
  border-color: #dd0000;
  border-style: solid;
  border-top-width: 1px;
  border-right-width: 2px;
  border-bottom-width: 3px;
  border-left-width: 4px;
}

.tester3 {
  border-color: #00dd00;
  border-style: inset;
  border-top-width: 5px;
  border-right-width: 6px;
  border-bottom-width: 1px;
  border-left-width: 2px;
}

SassMeister-rendered.html

<div class="tester"></div>
<div class="tester2"></div>
<div class="tester3"></div>