code.scss

.section-title {
  font-size: rem(28px);
  color: $blue;
  @include inverse-bottom-line(80%);
}

.collaborate-item:last-child {
  @include left-line(90%);
  padding-left: 10%;
}

.address-map {
  @include top-line(100%, .25);
  @include bottom-line(100%, .25);
}


lines.scss

// Lines
@mixin line($mode, $type, $size, $thickness) {
  $distance: (100% - $size) / 2;
  &:#{$type} {
    content : '';
    position: absolute;
    z-index: 1;
    @if $mode == horizontal {
      left: $distance; right: $distance;
      height: $thickness;
    } @else {
      top: $distance; bottom: $distance;
      width: $thickness;
    }
  }
}

@mixin line-gradient($pos, $opacity) {
  @include radial-gradient($pos, rgba(black, $opacity), rgba(black, 0));
}

@mixin left-line($size, $opacity: .15, $thickness: 10px) {
  @include line(vertical, before, $size, $thickness);
  &:before {
    left: 0;
    @include line-gradient(left center, $opacity);
  }
}

@mixin bottom-line($size, $opacity: .15, $thickness: 10px) {
  @include line(horizontal, after, $size, $thickness);
  &:after {
    bottom: 0;
    @include line-gradient(center bottom, $opacity);

  }
}

@mixin top-line($size, $opacity: .15, $thickness: 10px) {
  @include line(horizontal, before, $size, $thickness);
  &:before {
    top: 0;
    @include line-gradient(center top, $opacity);
  }
}

@mixin inverse-bottom-line($size, $opacity: .15, $thickness: 10px) {
  @include line(horizontal, after, $size, $thickness);
  &:after {
    bottom: -$thickness;
    @include line-gradient(center top, $opacity);
  }
}

@mixin hide-bottom-line {
  &:after {
    display: none;
  }
}