#tab_sign a {
  height: 41px;
  width: 41px;
  margin: 0;
  padding: 0;
}

#tab_sign a:link,
#tab_sign a:active,
#tab_sign a:visited {
  display: block;
  background-position: 0 1px;
  background-repeat: no-repeat;
}

#tab_sign a:hover{
  background-position: 0 -40px;
}