Fix mobile layout bug on ucr-ingress.com

ucr-ingress.com-mobile.css

/* All Smartphones in portrait and landscape ----------- */
@media only screen 
and (min-device-width : 320px) 
and (max-device-width : 480px) {
  #join_ucr {
    text-align: center;
    position : fixed;
    font-size: 0px;
    font-weight: bold;
    padding-top: 0;
    padding-bottom: 0;
  }

  #join_ucr a {
    display: block;
    margin-left: auto;
    margin-right:  auto;
    padding: 20px;
    font-size: 5vw;
    margin-top: 0;
    margin-bottom: 0; 
    border-radius: 15px;
  }
  
  #call_to_action  {
    margin-bottom: 15%;
  }
}