body {background-color: black;}

.container { 
  height: 600px;
  position: relative;
}

.center {
    display: block;
    margin-left: auto;
    margin-right: auto;
    width: 50%;
}

.vertical-center {
  margin: 0;
  position: absolute;
  top: 50%;
  left: 50%;
  -ms-transform: translate(-50%, -50%);
  transform: translate(-50%, -50%);
}