Css 垂直下拉菜单

我正在尝试创建一个下拉菜单类似于在这个网站上找到的

我已经创建了下拉菜单，但我不知道如何定位像在网站上找到的列表。和网站一样，我也想知道如何在标题下定位列表。非常感谢您提供的任何帮助

/* NAVIGATION START */

nav {
    display: block;
    width: 960px;
    margin: 100px auto;
    text-align: center;
}

nav select {
    display: none;
}

#menu {
    width: 608px;
    margin-top: 0px;
    margin-right: auto;
    margin-bottom: 0px;
    margin-left: auto;
    padding-top: 0px;
    padding-right: 0px;
    padding-bottom: 0px;
    padding-left: 0px;
}

#menu ul {
    margin: 0px;
    padding: 0px;
}

#menu ul li {
    background-color: #666;
    float: left;
    border: 1px solid #CCC;
    position: relative;
    list-style-type: none;
}

#menu ul li:hover ul {
    visibility: visible;
    background-color: #333;
}

#menu ul li a {
    font-family: "Trebuchet MS", Arial, Helvetica, sans-serif;
    font-size: 14px;
    line-height: 30px;
    color: #FFF;
    text-decoration: none;
    text-align: center;
    display: block;
    height: 30px;
    width: 150px;
}

#menu ul ul  {
    position: absolute;
    visibility: hidden;
    left: -1px;
    top: 31px;
}

#menu ul li:hover {
    background-color: #333;
}

#menu ul li ul li a:hover {
    background-color: #069;
}

#menu ul li a:hover {
    color: #0FF;
}

#leftmenu {
    position: absolute;
    left: 165px;
    top: 20px;
}

#rightmenu {
    position: absolute;
    right: 164px;
    top: 20px;
}

/* NAVIGATION END */

<nav> 
  <div id="menu">
    <ul id='leftmenu'>
      <li><a href="#">BOAT</a>
        <ul>
          <li><a href='#'>Specs & Boat Plans</a></li>
          <li><a href='#'>Itineraries</a></li>
          <li><a href='#'>Exteriors</a></li>
          <li><a href='#'>Diving & Water Toys</a></li>
          </ul>
        </li>
      </ul>
    <ul id='rightmenu'>
      <li><a href="#">LIFE ON BOARD</a>
        <ul>
          <li><a href='#'>Itineraries</a></li>
          <li><a href='#'>Dining</a></li>
          <li><a href='#'>Family Fun</a></li>
          <li><a href="#">Lifelong Learning</a></li>
          <li><a href="#">The Crew</a></li>
          </ul>
        </li>
      </ul>
    </div>
</nav>

---

以下是一些CSS帮助您入门：

/* NAVIGATION START */

nav {
    display: block;
    width: 960px;
    margin: 100px auto;
    text-align: center;
}

nav select {
    display: none;
}

#menu {
    width: 608px;
    margin-top: 0px;
    margin-right: auto;
    margin-bottom: 0px;
    margin-left: auto;
    padding-top: 0px;
    padding-right: 0px;
    padding-bottom: 0px;
    padding-left: 0px;
}

#menu ul {
    margin: 0px;
    padding: 0px;
}

#menu ul li {
    background-color: #666;
    float: left;
    border: 1px solid #CCC;
    position: relative;
    list-style-type: none;
}

#menu ul li:hover ul {
    visibility: visible;
}

#menu ul li a {
    font-family: "Trebuchet MS", Arial, Helvetica, sans-serif;
    font-size: 14px;
    line-height: 30px;
    color: #FFF;
    text-decoration: none;
    text-align: center;
    display: block;
    height: 30px;
    width: 150px;
}

#menu ul ul  {
    position: absolute;
    visibility: hidden;
    left: -1px;
    top: 31px;
}

#menu ul li:hover {
    background-color: #333;
}

#menu ul li ul li a:hover {
    background-color: #069;
}

#menu ul li a:hover {
    color: #0FF;
}

#leftmenu {
    position: absolute;
    left: 165px;
    top: 20px;
}
#leftmenu li>ul>li {
    margin:1em 0;
}
    #leftmenu li:nth-child(2) {
        margin-left:20px;
    }
    #leftmenu li:nth-child(3) {
        margin-left:40px;
    }
    #leftmenu li:nth-child(4) {
        margin-left:60px;
    }

#rightmenu {
    position: absolute;
    right: 164px;
    top: 20px;
}
#rightmenu li>ul>li {
    margin:1em 0;
}
    #rightmenu li:nth-child(2) {
        margin-left:-20px;
    }
    #rightmenu li:nth-child(3) {
        margin-left:-40px;
    }
    #rightmenu li:nth-child(4) {
        margin-left:-60px;
    }
    #rightmenu li:nth-child(5) {
        margin-left:-80px;
    }

和a.您可以简化

#menu {
    width: 608px;
    margin-top: 0px;
    margin-right: auto;
    margin-bottom: 0px;
    margin-left: auto;
    padding-top: 0px;
    padding-right: 0px;
    padding-bottom: 0px;
    padding-left: 0px;
}

到

为此。。。呃。。。级联效应，您可能需要使用类似

<li style="padding-left: some value here">

并且随着时间的推移而减少，因为你把它们浮到了正确的位置。此外，菜单必须与从最左边的菜单项到最右边的空间一样宽；它不能与一个菜单项一样宽

<li style="padding-left: some value here">