SOURCE

<div class="nav-wrapper container">
  <div class="nav">
    <div class="dropdown"><a>家用电器</a>
      <div class="megamenu">
        <p>电视</p>
        <p>空调</p>
      </div>
    </div>
    <div class="dropdown"><a>手机/运营商/数码</a>
      <div class="megamenu">
        <p>手机通讯</p>
        <p>运营商</p>
      </div>
    </div>
    <div class="dropdown"><a>电脑/办公</a>
      <div class="megamenu">
        <p>电脑整机</p>
        <p>电脑配件</p>
      </div>
    </div>
    <!-- repeat 5 more times -->
</div>

/* Global Base Styles and Resets */
* {
  box-sizing: border-box;
}

body {
  background-image: url(https://s3-us-west-2.amazonaws.com/s.cdpn.io/867725/black-wood-small.jpg);
  color: white;
}

/* Bootstrap features for responsiveness */
.container {
  margin: 0 auto;
  width: 100%;
}

/* THE BASIC NAVBAR ONLY */
.nav-wrapper {
  background-color: grey;
}

.nav {
  display: flex;
  justify-content: space-between;
  text-align: center;
  position: relative;
}

.dropdown {
  width: 100%;
  border-right: 1px solid black;
}
.dropdown:last-of-type {
  border-right: none;
}

a {
  color: white;
  width: 100%;
  display: block;
  padding: 10px;
  transition: all 0.3s ease 0.15s;
}
a:hover {
    background-color: red;
}

.megamenu {
  position: absolute;
  display: block;
  width: 100%;
  left: 0;
  top: 39px;
  opacity: 0;
  visibility: hidden;
  overflow: hidden;
  background: red;
  transition: all 0.3s ease 0.15s;
}

.dropdown:hover .megamenu {
  opacity: 1;
  visibility: visible;
  overflow: visible;
}