bootswatch-sass/bootswatch/bower_components/bootstrap/less/mixins/opacity.less

Bootswatch is a collection of themes for Bootstrap. SASS / SCSS edition

// Opacity

.opacity(@opacity) {
  opacity: @opacity;
  // IE8 filter
  @opacity-ie: (@opacity * 100);
  filter: ~"alpha(opacity=@{opacity-ie})";
}