sass-site/source/assets/css/components/_icons.scss

$os-icons: "icons/os-icons.png";

// TODO: Make these use a 16-base instead of 15.
%os-icons {
  @include square(15px);
  background: image-url($os-icons) 0 0 no-repeat;
  background-size: auto 15px;
  display: inline-block;
}
.mac-icon {
  @extend %os-icons;
  background-position: -35px 0;
}
.windows-icon {
  @extend %os-icons;
}
.linux-icon {
  @extend %os-icons;
  background-position: -65px 0;
}
.paid-icon {
  @extend %os-icons;
  background-position: -100px 0;
}