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$underline-color: #000;
$underline-distance: 5px;
$underline-thickness: 2px;

a.underline {
  position: relative;
  color: #000;
  text-decoration: none;
  padding-bottom: $underline-distance;
  &:hover, &.active {
    color: #000;
    &:before {
      width: 100%;
    }
  }
  &:before {
    content: "";
    position: absolute;
    width: 0%;
    height: $underline-thickness;
    bottom: 0;
    left: 0;

    background-color: $underline-color;
    transition: width .3s;
  }
}