.overlay-alert{
  display: table;
  width: 100%;
  height: 100%;
  background-color: rgba(0,0,0,0.7);
  position: absolute;
  top: 0;
  left: 0;
  z-index: 2;
  color: #ffffff;
  text-transform: uppercase;
  text-align: center;
}
.overlay-alert span{
  display: table-cell;
  vertical-align: middle;
}