<===> input.scss
.sprites-nav {
  color: red;
}

.sprites-nav_up {
  color: green;
}

.mw_nav_button {
  float: right;
  width: 30px;
  height: 30px;
  margin: 10px 10px 10px 0;
  overflow: hidden;
  &[data-ur-state="disabled"] {
    @extend .sprites-nav;
  }
  &[data-ur-state="enabled"] {
    @extend .sprites-nav_up;
  }
}

<===> output.css
.sprites-nav, .mw_nav_button[data-ur-state="disabled"] {
  color: red;
}

.sprites-nav_up, .mw_nav_button[data-ur-state="enabled"] {
  color: green;
}

.mw_nav_button {
  float: right;
  width: 30px;
  height: 30px;
  margin: 10px 10px 10px 0;
  overflow: hidden;
}

<===> output-dart-sass.css
.sprites-nav, .mw_nav_button[data-ur-state=disabled] {
  color: red;
}

.sprites-nav_up, .mw_nav_button[data-ur-state=enabled] {
  color: green;
}

.mw_nav_button {
  float: right;
  width: 30px;
  height: 30px;
  margin: 10px 10px 10px 0;
  overflow: hidden;
}