gnome-shell-dark-theme/gnome-shell-sass/widgets/_base.scss

// Links
.shell-link {
  color: $link_color;

  &:hover {
    color: st-lighten($link_color, 10%);
  }
}

// Outline for low res icons
.lowres-icon {
  icon-shadow: 0 1px 2px rgba(black, 0.2);
}

// Dropshadow for large icons
.icon-dropshadow {
  icon-shadow: 0 2px 4px rgba(black, 0.4);

  @if $contrast == 'high' {
    icon-shadow: none;
  }
}