Generated by SassMeister.com.

SassMeister-input-HTML.html

<hr class="rule">

SassMeister-input.sass

// ----
// Sass (v3.3.14)
// Compass (v1.0.1)
// ----

.rule
  position: relative
  width: 100%
  height: 1px
  color: rgba(white, 0.6)
  background-color: rgba(white, 0.6)
  border: 0

  &:after
    content: ""
    display: block
    position: absolute
    top: -8px
    left: 50%
    width: 0
    height: 0
    margin-left: -8.5px
    border-style: solid
    border-width: 9px 8px
    border-color: transparent #fff transparent #fff


// ignore
body
  padding: 50px
  background: #777

SassMeister-output.css

.rule {
  position: relative;
  width: 100%;
  height: 1px;
  color: rgba(255, 255, 255, 0.6);
  background-color: rgba(255, 255, 255, 0.6);
  border: 0;
}
.rule:after {
  content: "";
  display: block;
  position: absolute;
  top: -8px;
  left: 50%;
  width: 0;
  height: 0;
  margin-left: -8.5px;
  border-style: solid;
  border-width: 9px 8px;
  border-color: transparent white transparent white;
}

body {
  padding: 50px;
  background: #777777;
}

SassMeister-rendered.html

<hr class="rule">