nav ul {
  background: #333;
  list-style: none;
  margin: 0;
  padding: 0;
}

nav > ul {
  display: flex;
}

nav li {
  position: relative;
}

nav li > ul {
  display: none;
  position: absolute;
}

nav li > ul ul {
  left: 100%;
  top: 0;
}

nav a {
  color: #fff;
  display: block;
  font-family: Helvetica, Arial, sans-serif;
  font-size: 18px;
  padding: 10px 15px;
  text-decoration: none;
  transition: all 0.3s;
  white-space: nowrap;
}

nav li:hover > a {
  background: #eee;
  color: #333;
}

nav li:hover > ul {
  display: block;
}