body 
.overlay {
  height: 0%;
  width: 100%;
  position: fixed;
  z-index: 100;
  top: 0;
  left: 0;
  background-color: rgb(180,0,0);
  background-color: rgba(180,0,0,1);
  overflow-y: hidden;
  transition: 0.5s;
}

.overlay-content {
  position: relative;
  top: 20%;
  width: 100%;
  text-align: center;
  margin-top: 30px;
  z-index: 100;
}

.overlay a {
  transition: 0.3s;
}

.overlay a:hover, .overlay a:focus {
  color: #F1F1F1;
  opacity: 0.8;
}

.overlay .closebtn {
  position: absolute;
  top: 20px;
  right: 45px; 
}

@media screen and (max-height: 450px) {
  .overlay {z-index: 100; overflow-y: auto;}
  .overlay .closebtn {
  top: 10px;
  right: 20px;
  }
}