.btn-enter {
  display: none;
  margin: 0 auto;
  padding:5px 10px;
  background: #00CC33;
  margin-top: 25px;
  color: white;
  font-size: 24px;
}
.btn-close {
  display: none;
  position:absolute;
  top:0;
  right:0;font-size:30px;
  z-index: 900
}
#game-wrap {
  display: flex;
  justify-content: center;
  align-items: center;
  line-height: normal;
}

@media (max-width: 650px) {
  .btn-enter, .btn-close {display: block;}
  #game-wrap {display:none;position: fixed;top: 0;left: 0;right: 0;bottom: 0;z-index: 100}
}