Simple CSS Dropdown Menu with Hover and :focus-within and Focus states and ARIA

index.html

<nav role="navigation">
  <ul>
    <li><a href="#">One</a></li>
    <li><a href="#" aria-haspopup="true">Two</a>
      <ul class="dropdown" aria-label="submenu">
        <li><a href="#">Sub-1</a></li>
        <li><a href="#">Sub-2</a></li>
        <li><a href="#">Sub-3</a></li>
      </ul>
    </li>
    <li><a href="#">Three</a></li>
  </ul>
</nav>

styles.css

a {
  text-decoration: none;
}

nav {
	font-family: monospace;
}

ul {
  background: darkorange;
	list-style: none;
	margin: 0;
	padding-left: 0;
}

li {
	color: #fff;
  background: darkorange;
	display: block;
	float: left;
	padding: 1rem;
	position: relative;
	text-decoration: none;
  transition-duration: 0.5s;
}
  
li a {
  color: #fff;
}

li:hover,
li:focus-within {
	background: red;
	cursor: pointer;
}

li:focus-within a {
  outline: none;
}

ul li ul {
	background: orange;
	visibility: hidden;
  opacity: 0;
  min-width: 5rem;
	position: absolute;
  transition: all 0.5s ease;
  margin-top: 1rem;
	left: 0;
  display: none;
}

ul li:hover > ul,
ul li:focus-within > ul,
ul li ul:hover,
ul li ul:focus {
   visibility: visible;
   opacity: 1;
   display: block;
}

ul li ul li {
	clear: both;
  width: 100%;
}