drupal/core/themes/bartik/css/components/feed-icon.css

/**
 * @file
 * Feed icon styles for Bartik.
 */

.feed-icon {
  display: inline-block;
  padding-bottom: 2px;
  border-bottom: 1px solid transparent;
}

.feed-icon:focus,
.feed-icon:hover {
  border-color: #018fe2;
}