<div class="middle">
  <ul class="menu">
    <li class="item" id="profile">
      <a href="#profile" class="button"><i class="far fa-user"></i>Profile</a>
      <div class="smenu">
        <a href="#">Posts</a>
        <a href="#">Picture</a>
      </div>
    </li>

    <li class="item" id="messages">
      <a href="#messages" class="button"><i class="far fa-envelope"></i>Messages</a>
      <div class="smenu">
        <a href="#">New</a>
        <a href="#">Sent</a>
        <a href="#">Spam</a>
      </div>
    </li>

    <li class="item" id="settings">
      <a href="#settings" class="button"><i class="fas fa-cog"></i>Settings</a>
      <div class="smenu">
        <a href="#">Password</a>
        <a href="#">Language</a>
      </div>
    </li>

    <li class="item">
      <a href="#" class="button"><i class="fas fa-sign-out-alt"></i>Logout</a>
    </li>
  </ul>
</div>

* {
  margin: 0;
  padding: 0;
  font-family: sans-serif;
  list-style: none;
  text-decoration: none;
}

.middle {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

.menu {
  width: 300px;
  border-radius: 8px;
  overflow: hidden;
}

.item {
  border-top: 1px solid #2980b9;
  overflow: hidden;
}

.button {
  display: block;
  padding: 16px 20px;
  background: #3498db;
  color: white;
  position: relative;
}

.button::before {
  content: '';
  position: absolute;
  width: 14px;
  height: 14px;
  background: #3498db;
  left: 20px;
  bottom: -7px;
  transform: rotate(45deg);
}

.button i {
  margin-right: 10px;
}

.smenu {
  background: #333;
  overflow: hidden;
  max-height: 0;
  transition: max-height 0.3s;
}

.smenu a {
  display: block;
  padding: 16px 26px;
  color: white;
  font-size: 14px;
  margin: 4px 0;
  position: relative;
}

.smenu a::before {
  content: '';
  position: absolute;
  width: 6px;
  height: 100%;
  background: #3498db;
  left: 0;
  top: 0;
  transition: 0.3s;
  opacity: 0;
}

.smenu a:hover::before{
  opacity: 1;
}

.item:target .smenu{
  max-height: 10em;
}