.menu {
  position: fixed;
  display: table;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: rgba(0, 0, 0, 0.8);
  -webkit-transition: all 0.5s;
  transition: all 0.5s;
  visibility: hidden;
  opacity: 0;
  position: absolute;
  z-index: 9999;
}

.open .menu {
  -webkit-transition: all 0.5s;
  transition: all 0.5s;
  visibility: visible;
  opacity: 1;
}