问嵌套的ul和ol结束标记放置

EN

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-size: 10px;
  overflow-x: hidden;
}

header {
  background-color: #f88752;
  position: relative;
  height: 50px;
  width: 100%;
}

nav {
    height: 100%;
}

.first-list,
.second-list {
  list-style-type: none;
  display: flex;
  align-items: center;
  justify-content: center;
}

.first-list {
  height: 100%;
}

.first-list .list1-item {
  margin: 0 10px;
  cursor: pointer;
  color: #f1f1f1;
  font-size: 1.3rem;
}

.second-list {
  position: absolute;
  flex-direction: column;
  left: -100%;
  transform: translate(-50%, 0);
  top: 65px;
  background-color: #f88752;
  width: 400px;
  height: 70px;
  border-radius: 5px;
  transition: all 0.2s;
}

.second-list .list2-item {
  font-size: 1.2rem;
}

#myBtn:hover ~ .second-list {
  left: 50%;
}

<header>
  <nav>
    <ul class="first-list">
      <li class="list1-item">Home</li>
      <li class="list1-item">Gallery</li>
      <li class="list1-item">About</li>
      <li class="list1-item" id="myBtn">Contact</li>
      <ul class="second-list">
        <li class="list2-item">+123456789</li>
        <li class="list2-item">example@hotmail.com</li>
      </ul>
    </ul>
  </nav>
</header>

  li{
    padding-left: 30px;
  }

<ul>
  <li>first item</li>
  <!-- No closing li tag in next line -->
  <li>second item
    <ul>
      <li>first subitem of second item</li>
    </ul>
  <!-- li closing tag in next line -->
  </li> 
</ul>

<ul>
  <li>first item</li>
  <!-- Closing li tag in next line like normal -->
  <li>second item</li>
  <ul>
    <li>first subitem of second item</li>
  </ul>
</ul>