.menu,
.submenu {
  list-style: none;
  padding: 0;
  margin: 0;
}

.menu > li {
  position: relative;
}

.submenu {
  display: none;
  position: absolute;
  top: 100%;
  left: 0;
  background: white;
  border: 1px solid #ccc;
}

.menu > li:hover .submenu {
  display: block;
}