silverstripe-dms/scss/_mixins.scss

//** Generate a state for an active list item link
//
// @param {string} $color - the colour to use for the border
// @param {string} $size  - the size the border should be, e.g. "8px"
@mixin dmsdocument-actions-active($color, $size: "4px") {
  border-bottom: #{$size} solid #{$color};
}