style.css

.modal {
  position: fixed; /* Stay in place */
  z-index: 1; /* Sit on top */
  left: 0;
  top: 0;
  width: 100%; /* Full width */
  height: 100%; /* Full height */
  overflow: auto; /* Enable scroll if needed */
  background-color: rgb(0, 0, 0); /* Fallback color */
  background-color: rgba(0, 0, 0, 0.452); /* Black w/ opacity */
}

.modal-content {
  font-size: 25px;
  top: 50%;
  left: 50%;
  width: 500px;
  height: 500px;
  background: rgb(255, 255, 255);
  position: absolute;
  transform: translate(-50%, -50%);
  background-image: url(https://media1.tenor.com/images/376c2f0d7e661d0097bd5555f61f5d40/tenor.gif?itemid=5454470);
  background-repeat: no-repeat;
  background-position: center;
}