MediaWiki:Common.css

a {
  text-decoration: none !important;
}

a:hover {
  text-decoration: underline; /* optional hover effect */
}

#f-poweredbyico img {
  display: none !important;
}

#f-poweredbyico::after {
  content: "";
  display: inline-block;
  width: 88px;
  height: 31px;
  background-image: url("/skins/Vector/resources/images/poweredby_mediawiki_88x31.png");
  background-size: contain;
  background-repeat: no-repeat;
}