Tree menu

<link rel='stylesheet prefetch' href='https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.4.0/css/font-awesome.min.css'/>
<style class="cp-pen-styles">* {
  box-sizing: border-box;
}
ul {
  margin: 0;
  padding: 0;
  list-style-type: auto;
}
a {
  display: block;
  padding: .2rem 0;
  color: #000;
  font-size: .875rem;
  text-decoration: none;
  float: left;
  position: relative;
  white-space: nowrap;
}
a:hover {
  color: #992211;
  text-decoration: underline;
}
h4 {
  margin: .5rem 0 .75rem;
  padding-bottom: .5rem;
  border-bottom: 1px solid #ddd;
  font-size: 1.25rem;
  font-weight: normal;
}
h5 {
  margin: 0;
  margin-bottom: .5rem;
  font-size: .875rem;
}
nav::after {
  content: '';
  display: block;
  clear: both;
}
.menu {
  display: inline-block;
  border-radius: .2rem;
  background: #fff;
  position: relative;
  z-index: 2;
}
.menu:hover {
  box-shadow: 0 0 0.35rem 0 rgba(0, 0, 0, 0.5);
  position: absolute;
}
.menu:hover > li {
  display: block;
}
.menu:hover > li:first-child {
  border-color: transparent;
  border-bottom: none;
  border-radius: .2rem .2rem 0 0;
  background-color: #eee;
  box-shadow: none;
  position: relative;
  z-index: 1;
  color: #444;
  cursor: default;
}
.menu:hover > li:first-child::after {
  content: '\f106';
}
.menu:hover > li:last-child {
  border-radius: 0 0 .2rem .2rem;
}
.menu:hover + .temp::after {
  display: block;
}
.menu > li {
  display: none;
  width: 12rem;
  margin: 0;
  border-right: 1px solid #bbb;
}
.menu > li:first-child {
  display: block;
  padding: .65rem .65rem;
  border: 1px solid #bbb;
  border-radius: .20rem;
  background: #fff;
  box-shadow: 0 3px 3px -3px rgba(0, 0, 0, 0.5);
  color: #000;
  font-weight: bold;
  font-size: .875rem;
  cursor: pointer;
}
.menu > li:first-child::after {
  content: '\f107';
  float: right;
  font: bold 1rem fontAwesome;
}
.menu > li:not(:first-child):hover {
  width: calc(898px - 6rem);
  border-right: none;
}
.menu > li:nth-child(2):hover::before {
  content: '';
  display: block;
  width: 12rem;
  height: 3rem;
  border: 1px solid transparent;
  position: absolute;
  top: 0;
  z-index: 10;
}
li h3 {
  width: 12rem;
  margin: 0;
  padding: .65rem .75rem;
  border: 1px solid transparent;
  border-width: 1px 0;
  background: #fff;
  position: relative;
  z-index: 10;
  font-size: .875rem;
  font-weight: normal;
  cursor: default;
}
li:last-child h3 {
  border-radius: 0 0 .2rem .2rem;
  color: darkred;
}
li:last-child:hover h3 {
  border-bottom-color: transparent;
  border-radius: 0 0 0 .2rem;
}
li:hover h3 {
  width: calc(12rem + 1px);
  border-color: #bbb;
}
li:hover div {
  display: block;
}
li div {
  display: none;
  width: calc(896px - 6rem - 12rem);
  padding: 1rem 1.2rem;
  border-left: 1px solid #bbb;
  border-radius: 0 .2rem .2rem 0;
  background: #fff;
  position: absolute;
  top: 0;
  bottom: 0;
  left: 12rem;
  z-index: 1;
}
main {
  display: -webkit-box;
  display: -webkit-flex;
  display: -ms-flexbox;
  display: flex;
  width: 100%;
  height: 15rem;
  margin-top: 2rem;
  padding: 1rem;
  background: #ccc;
  position: relative;
  z-index: 1;
  clear: both;
}
main p {
  margin: auto;
  color: #555;
  text-transform: uppercase;
  letter-spacing: 1px;
}
::selection{background:#d58151;color:#fff;text-shadow:none}
::-moz-selection{background:#d58151;color:#fff;text-shadow:none}
@media (max-width: 60rem) {
  .temp {
    width: 67%;
  }
}
</style>
<nav>
  <ul class="menu">
    <li>THỰC ĐƠN :D
    </li>
    <li>
      <h3>Truyện cười</h3>
      <div style="text-align: justify;overflow:auto;">
        <h4>Sưu tầm</h4>
        noidung
      </div>
    </li>
    <li>
      <h3>Hình Vui</h3>
      <div style="text-align: justify;overflow:auto;">
        <h4>Ảnh sưu tầm</h4>
        noi dung
      </div>
    </li>
    <li>
      <h3>Toys</h3>
      <div>
        <h4>Brands</h4>
        noidung
      </div>
    </li>   
    <li>
      <h3>Sport & Leisure</h3>
      <div style="text-align: justify;">
        <h4>Sport</h4>
        noidung
      </div>
    </li>
    <li>
      <h3>Home & Cooking</h3>
      <div>
        <h4>Cooking</h4>
        noidung
      </div>
    </li>   
    <li>
      <h3>Garden & DIY</h3>
      <div style="text-align: justify;">
        <h4>Garden</h4>
        noidung
      </div>
    </li>
    <li>
      <h3>Gifts</h3>
      <div style="text-align: justify;">
        <h4>Gifts</h4>
        noidung
      </div>
    </li>
    <li>
      <h3>Specials</h3>
      <div style="text-align: justify;">
        <h4>Specials</h4>
        noidung
      </div>
    </li>
    <li>
      <h3>Specials 1</h3>
      <div style="text-align: justify;">
        <h4>Specials 1</h4>
        noidung
      </div>
    </li>
    <li>
      <h3>Specials 2</h3>
      <div style="text-align: justify;">
        <h4>Specials 2</h4>
        noidung
      </div>
    </li>
    <li>
      <h3>Specials 3</h3>
      <div style="text-align: justify;">
        <h4>Specials 3</h4>
        noidung
      </div>
    </li>
    <li>
      <h3>Specials 4</h3>
      <div style="text-align: justify;">
        <h4>Specials 4</h4>
        noidung
      </div>
    </li>
  </ul>
</nav>