.menu {
  position: absolute;
  opacity: 1;
  top: 20px;
  left: 20px;
  width: 200px;
  height: 100px;
  z-index: 10000;
}
#menu-bar {
  opacity: 0.5;
}
.menu-content {
  visibility: hidden;
}
.menu:hover .menu-content{
  visibility: visible;
}
.menu:hover  #menu-bar{
  opacity: 1;
}