Replace flag links by image icons in drupal 7

replace_flag_links.md

.flag-published-or-reject .flag-action {
  background: url(../images/publish.png) no-repeat center center;
  border:none;
  width: 120px;
  height: 25px;
  margin-right: 20px;
  float: left;
  color: transparent;
}
.flag-published-or-reject .unflag-action {
  background: url(../images/unpublish.png) no-repeat center center;
  border:none;
  width: 120px;
  height: 25px;
  margin-right: 20px;
  float: left;
  color: transparent;
}

".flag-published-or-reject" is class for flag "flag-published-or-reject".