如何使用CSS實現的大型下拉菜單

<nav>
 <ul class="container ul-reset">
 <li><a href='#'>Home</a></li>
 <li class='droppable'>
 <a href='#'>Category One</a>
 <p class='mega-menu'>
 <p class="container cf">
 <ul class="ul-reset">
 <h3>Heading 1</h3>
 <li><a href='#'>Category One Sublink</a></li>
 <li><a href='#'>Category One Sublink</a></li>
 <li><a href='#'>Category One Sublink</a></li>
 <li><a href='#'>Category One Sublink</a></li>
 <li><a href='#'>Category One Sublink</a></li>
 </ul><!-- .ul-reset -->
 <ul class="ul-reset">
 <h3>Heading 2</h3>
 <li><a href='#'>Category One Sublink</a></li>
 <li><a href='#'>Category One Sublink</a></li>
 <li><a href='#'>Category One Sublink</a></li>
 <li><a href='#'>Category One Sublink</a></li>
 <li><a href='#'>Category One Sublink</a></li>
 </ul><!-- .ul-reset -->
 <ul class="ul-reset">
 <h3>Heading 3</h3>
 <li><a href='#'>Category One Sublink</a></li>
 <li><a href='#'>Category One Sublink</a></li>
 <li><a href='#'>Category One Sublink</a></li>
 <li><a href='#'>Category One Sublink</a></li>
 <li><a href='#'>Category One Sublink</a></li>
 </ul><!-- .ul-reset -->
 <ul class="ul-reset">
 <h3>Heading 4</h3>
 <li><img src="http://placehold.it/205x172"></li>
 </ul>
 </p><!-- .container -->
 </p><!-- .mega-menu -->
 </li><!-- .droppable -->
 <li class='droppable'>
 <a href='#'>Category Two</a>
 <p class='mega-menu'>
 <p class="container cf">
 <ul class="ul-reset">
 <h3>Heading 1</h3>
 <li><a href='#'>Category Two Sublink</a></li>
 <li><a href='#'>Category Two Sublink</a></li>
 <li><a href='#'>Category Two Sublink</a></li>
 <li><a href='#'>Category Two Sublink</a></li>
 <li><a href='#'>Category Two Sublink</a></li>
 </ul><!-- .ul-reset -->
 <ul class="ul-reset">
 <h3>Heading 2</h3>
 <li><a href='#'>Category Two Sublink</a></li>
 <li><a href='#'>Category Two Sublink</a></li>
 <li><a href='#'>Category Two Sublink</a></li>
 <li><a href='#'>Category Two Sublink</a></li>
 <li><a href='#'>Category Two Sublink</a></li>
 </ul><!-- .ul-reset -->
 <ul class="ul-reset">
 <h3>Heading 3</h3>
 <li><a href='#'>Category Two Sublink</a></li>
 <li><a href='#'>Category Two Sublink</a></li>
 <li><a href='#'>Category Two Sublink</a></li>
 <li><a href='#'>Category Two Sublink</a></li>
 <li><a href='#'>Category Two Sublink</a></li>
 </ul><!-- .ul-reset -->
 <ul class="ul-reset">
 <h3>Heading 4</h3>
 <li><a href='#'>Category Two Sublink</a></li>
 <li><a href='#'>Category Two Sublink</a></li>
 <li><a href='#'>Category Two Sublink</a></li>
 <li><a href='#'>Category Two Sublink</a></li>
 <li><a href='#'>Category Two Sublink</a></li>
 </ul><!-- .ul-reset -->
 </p><!-- .container -->
 </p><!-- .mega-menu-->
 </li><!-- .droppable -->
 <li><a href='#'>Category Three</a></li>
 <li><a href='#'>Category Four</a></li>
 <li><a href='#'>Category Five</a></li>
 <li><a href='#'>Category Six</a></li>
 </ul><!-- .container .ul-reset -->
</nav>

/* #Resets
–––––––––––––––––––––––––––––––––––––––––––––––––– */
html {box-sizing: border-box;}
*, *:before, *:after {box-sizing: inherit; }
/* #Universal and Default Styles
–––––––––––––––––––––––––––––––––––––––––––––––––– */
body {
 background: url(../img/black-wood-small.jpg);
 color: #ddd;
 font-family: "Open Sans", sans-serif;
 font-size: 14px;
 line-height: 1;
 margin: 0;
 padding: 0;
 text-align: center;
}
a {text-decoration: none;}
h1 {
 font-size: 40px;
 font-weight: 700;
 margin-bottom: 20px;
 margin-top: 20px;
}
h2 {
 font-size: 15px;
 font-weight: 600;
 margin-bottom: 30px;
 margin-top: 10px;
}
.container {
 margin: auto;
 width: 940px;
}
.ul-reset {
 padding-left: 0;
 margin-top: 0;
 margin-bottom: 0;
 list-style: none;
}
/* #Navigation Styles
–––––––––––––––––––––––––––––––––––––––––––––––––– */
nav {
 background: #424242;
 font-size: 0;
 position: relative;
}
nav > ul > li {
 display: inline-block;
 font-size: 14px;
 padding: 0 15px;
 position: relative;
}
nav > ul > li:first-child {padding-left: 0;}
nav > ul > li:last-child {padding-right: 0;}
nav > ul > li > a {
 color: #fff;
 display: block;
 position: relative;
 padding: 20px 0;
 border-bottom: 3px solid transparent;
}
nav > ul > li:hover > a {
 color: #69aae0; 
 border-bottom: 3px solid #69aae0;
}
/* #Mega Menu Styles
–––––––––––––––––––––––––––––––––––––––––––––––––– */
.mega-menu {
 background: #f0f0f0;
 display: none;
 left: 0;
 position: absolute;
 text-align: left;
 width: 100%;
}
.mega-menu h3 {color: #444;}
.mega-menu ul {
 float: left;
 margin-bottom: 20px;
 margin-right: 40px;
 width: 205px;
}
.mega-menu ul:last-child {margin-right: 0;}
.mega-menu a {
 border-bottom: 1px solid #ddd;
 color: #4ea3d8;
 display: block;
 padding: 10px 0;
}
.mega-menu a:hover {color: #2d6a91;}
/* #Droppable Class Styles
–––––––––––––––––––––––––––––––––––––––––––––––––– */
.droppable {position: static;}
.droppable > a:after {
 content: "\f107";
 font-family: FontAwesome;
 font-size: 12px;
 padding-left: 6px;
 position: relative;
 top: -1px;
}
.droppable:hover .mega-menu {display: block;}
/* #Browser Clearfix
–––––––––––––––––––––––––––––––––––––––––––––––––– */
.cf:before,
.cf:after {
 content: " "; /* 1 */
 display: table; /* 2 */
}
.cf:after {clear: both;}