drupal/core/modules/system/css/components/clearfix.module.css

/**
 * @file
 * Float clearing.
 *
 * Based on the micro clearfix hack by Nicolas Gallagher, with the :before
 * pseudo selector removed to allow normal top margin collapse.
 *
 * @see http://nicolasgallagher.com/micro-clearfix-hack
 */

.clearfix:after {
  display: table;
  clear: both;
  content: "";
}