Pure CSS multi-level drop-down menu

Solution 1:

.third-level-menu
{
    position: absolute;
    top: 0;
    right: -150px;
    width: 150px;
    list-style: none;
    padding: 0;
    margin: 0;
    display: none;
}

.third-level-menu > li
{
    height: 30px;
    background: #999999;
}
.third-level-menu > li:hover { background: #CCCCCC; }

.second-level-menu
{
    position: absolute;
    top: 30px;
    left: 0;
    width: 150px;
    list-style: none;
    padding: 0;
    margin: 0;
    display: none;
}

.second-level-menu > li
{
    position: relative;
    height: 30px;
    background: #999999;
}
.second-level-menu > li:hover { background: #CCCCCC; }

.top-level-menu
{
    list-style: none;
    padding: 0;
    margin: 0;
}

.top-level-menu > li
{
    position: relative;
    float: left;
    height: 30px;
    width: 150px;
    background: #999999;
}
.top-level-menu > li:hover { background: #CCCCCC; }

.top-level-menu li:hover > ul
{
    /* On hover, display the next level's menu */
    display: inline;
}


/* Menu Link Styles */

.top-level-menu a /* Apply to all links inside the multi-level menu */
{
    font: bold 14px Arial, Helvetica, sans-serif;
    color: #FFFFFF;
    text-decoration: none;
    padding: 0 0 0 10px;

    /* Make the link cover the entire list item-container */
    display: block;
    line-height: 30px;
}
.top-level-menu a:hover { color: #000000; }
<ul class="top-level-menu">
    <li><a href="#">About</a></li>
    <li><a href="#">Services</a></li>
    <li>
        <a href="#">Offices</a>
        <ul class="second-level-menu">
            <li><a href="#">Chicago</a></li>
            <li><a href="#">Los Angeles</a></li>
            <li>
                <a href="#">New York</a>
                <ul class="third-level-menu">
                    <li><a href="#">Information</a></li>
                    <li><a href="#">Book a Meeting</a></li>
                    <li><a href="#">Testimonials</a></li>
                    <li><a href="#">Jobs</a></li>
                </ul>
            </li>
            <li><a href="#">Seattle</a></li>
        </ul>
    </li>
    <li><a href="#">Contact</a></li>
</ul>


I have also put together a live demo that's available to play with HERE

Solution 2:

body{margin:0px;}
.example {
    width:980px;
    height:40px;
    margin:0px auto;
 position:absolute;
 margin-bottom:60px;
 top:95px;
}

.menuholder {
    float:left;
    font:normal bold 11px/35px verdana, sans-serif;
    overflow:hidden;
    position:relative;
}
.menuholder .shadow {
    -moz-box-shadow:0 0 20px rgba(0, 0, 0, 1);
    -o-box-shadow:0 0 20px rgba(0, 0, 0, 1);
    -webkit-box-shadow:0 0 20px rgba(0, 0, 0, 1);
    background:#888;
    box-shadow:0 0 20px rgba(0, 0, 0, 1);
    height:10px;
    left:5%;
    position:absolute;
    top:-9px;
    width:100%;
    z-index:100;
}
.menuholder .back {
    -moz-transition-duration:.4s;
    -o-transition-duration:.4s;
    -webkit-transition-duration:.4s;
    background-color:rgba(0, 0, 0, 0.88);
    height:0;
    width:980px; /*100%*/
}
.menuholder:hover div.back {
    height:280px;
}
ul.menu {
    display:block;
    float:left;
    list-style:none;
    margin:0;
    padding:0 125px;
    position:relative;
}
ul.menu li {
    float:left;
    margin:0 10px 0 0;
}
ul.menu li > a {
    -moz-border-radius:0 0 10px 10px;
    -moz-box-shadow:2px 2px 4px rgba(0, 0, 0, 0.9);
    -moz-transition:all 0.3s ease-in-out;
    -o-border-radius:0 0 10px 10px;
    -o-box-shadow:2px 2px 4px rgba(0, 0, 0, 0.9);
    -o-transition:all 0.3s ease-in-out;
    -webkit-border-bottom-left-radius:10px;
    -webkit-border-bottom-right-radius:10px;
    -webkit-box-shadow:2px 2px 4px rgba(0, 0, 0, 0.9);
    -webkit-transition:all 0.3s ease-in-out;
    border-radius:0 0 10px 10px;
    box-shadow:2px 2px 4px rgba(0, 0, 0, 0.9);
    color:#eee;
    display:block;
    padding:0 10px;
    text-decoration:none;
    transition:all 0.3s ease-in-out;
}
ul.menu li a.red {
    background:#a00;
}
ul.menu li a.orange {
    background:#da0;
}
ul.menu li a.yellow {
    background:#aa0;
}
ul.menu li a.green {
    background:#060;
}
ul.menu li a.blue {
    background:#073263;
}
ul.menu li a.violet {
    background:#682bc2;
}
.menu li div.subs {
    left:0;
    overflow:hidden;
    position:absolute;
    top:35px;
    width:0;
}
.menu li div.subs dl {
    -moz-transition-duration:.2s;
    -o-transition-duration:.2s;
    -webkit-transition-duration:.2s;
    float:left;
    margin:0 130px 0 0;
    overflow:hidden;
    padding:40px 0 5% 2%;
    width:0;
}
.menu dt {
    color:#fc0;
    font-family:arial, sans-serif;
    font-size:12px;
    font-weight:700;
    height:20px;
    line-height:20px;
    margin:0;
    padding:0 0 0 10px;
    white-space:nowrap;
}
.menu dd {
    margin:0;
    padding:0;
    text-align:left;
}
.menu dd a {
    background:transparent;
    color:#fff;
    font-size:12px;
    height:20px;
    line-height:20px;
    padding:0 0 0 10px;
    text-align:left;
    white-space:nowrap;
    width:80px;
}
.menu dd a:hover {
    color:#fc0;
}
.menu li:hover div.subs dl {
    -moz-transition-delay:0.2s;
    -o-transition-delay:0.2s;
    -webkit-transition-delay:0.2s;
    margin-right:2%;
    width:21%;
}
ul.menu li:hover > a,ul.menu li > a:hover {
    background:#aaa;
    color:#fff;
    padding:10px 10px 0;
}
ul.menu li a.red:hover,ul.menu li:hover a.red {
    background:#c00;
}
ul.menu li a.orange:hover,ul.menu li:hover a.orange {
    background:#fc0;
}
ul.menu li a.yellow:hover,ul.menu li:hover a.yellow {
    background:#cc0;
}
ul.menu li a.green:hover,ul.menu li:hover a.green {
    background:#080;
}
ul.menu li a.blue:hover,ul.menu li:hover a.blue {
    background:#00c;
}
ul.menu li a.violet:hover,ul.menu li:hover a.violet {
background:#8a2be2;
}
.menu li:hover div.subs,.menu li a:hover div.subs {
    width:100%;
}
<div class="example" align="center">
    <div class="menuholder">
        <ul class="menu slide">
            <li><a href="index.php?id=1" class="blue">Home</a></li>
        <li><a href="index.php?id=14" class="blue">About Us</a></li>
            <li><a href="index.php?id=4" class="blue">Mens</a>
                <div class="subs">
                    <dl>
                        <dd><a href="index.php?id=15">Coats & Jackets</a></dd>
                        <dd><a href="index.php?id=22">Chinos</a></dd>
                        <dd><a href="index.php?id=23">Jeans</a></dd>
                        <dd><a href="index.php?id=24">Jumpers & Cardigans</a></dd>
                        <dd><a href="index.php?id=25">Linen</a></dd>
                    </dl>
                    <dl>
                        <dd><a href="index.php?id=26">Polo Shirts</a></dd>
                        <dd><a href="index.php?id=16">Shirts Casual</a></dd>
                        <dd><a href="index.php?id=27">Shirts Formal</a></dd>
                        <dd><a href="index.php?id=28">Shorts</a></dd>
                        <dd><a href="index.php?id=18">Sportswear</a></dd>
                    </dl>
                    <dl>
                        <dd><a href="index.php?id=19">Tops & T-Shirts</a></dd>
                        <dd><a href="index.php?id=20">Trousers Casual</a></dd>
                        <dd><a href="index.php?id=29">Trousers Formal</a></dd>
                        <dd><a href="index.php?id=30">Nightwear</a></dd>
                        <dd><a href="index.php?id=17">Socks</a></dd>
                    </dl>
                    <dl>
                        <dd><a href="index.php?id=21">Underwear</a></dd>
                        <dd><a href="index.php?id=31">Swimwear</a></dd>
                    </dl>
                </div>
            </li>
            <!--menu-->
                        <li><a href="index.php?id=5" class="blue">Ladie's</a>
                <div class="subs">
                    <dl>
                          <dd><a href="index.php?id=32">Coats & Jackets</a></dd>
                          <dd><a href="index.php?id=33">Dresses</a></dd>
                          <dd><a href="index.php?id=34">Jeans</a></dd>
                          <dd><a href="index.php?id=35">Jumpers & Cardigans</a></dd>
                          <dd><a href="index.php?id=36">Jumpsuits</a></dd>
                    </dl>
                    <dl>
                        <dd><a href="index.php?id=37">Leggings & Jeggings</a></dd>
                          <dd><a href="index.php?id=38">Linen</a></dd>
                          <dd><a href="index.php?id=39">Lingerie & Underwear</a></dd>
                          <dd><a href="index.php?id=40">Maternity Wear</a></dd>
                          <dd><a href="index.php?id=41">Nightwear</a></dd>
                    </dl>
                    <dl>
                     <dd><a href="index.php?id=42">Shorts</a></dd>
                          <dd><a href="index.php?id=43">Skirts</a></dd>
                          <dd><a href="index.php?id=44">Sportswear</a></dd>
                          <dd><a href="index.php?id=45">Suits & Tailoring</a></dd>
                          <dd><a href="index.php?id=46">Swimwear & Beachwear</a></dd>
                    </dl>
                    <dl>
                          <dd><a href="index.php?id=47">Thermals</a></dd>
                          <dd><a href="index.php?id=48">Tops & T-Shirts</a></dd>
                          <dd><a href="index.php?id=49">Trousers & Chinos</a></dd>
                          <dd><a href="index.php?id=50">Socks</a></dd>
                    </dl>
                </div>
            </li><!--menu end-->
                        <!--menu-->
                        <li><a href="index.php?id=7" class="blue">Girls</a>
                <div class="subs">
                    <dl>
                            <dd><a href="index.php?id=51">Coats & Jackets</a></dd>
                          <dd><a href="index.php?id=52">Dresses</a></dd>
                          <dd><a href="index.php?id=53">Jeans</a></dd>
                          <dd><a href="index.php?id=54">Joggers & Sweatshirts</a></dd>
                          <dd><a href="index.php?id=55">Jumpers & Cardigans</a></dd>
                    </dl>
                    <dl>
                                <dd><a href="index.php?id=56">Jumpsuits & Playsuits</a></dd>
                              <dd><a href="index.php?id=57">Leggings</a></dd>
                              <dd><a href="index.php?id=58">Nightwear</a></dd>
                              <dd><a href="index.php?id=59">Shorts</a></dd>
                              <dd><a href="index.php?id=60">Skirts</a></dd>
                    </dl>
                    <dl>
                              <dd><a href="index.php?id=61">Swimwear</a></dd>
                              <dd><a href="index.php?id=62">Tops & T-Shirts</a></dd>
                              <dd><a href="index.php?id=63">Trousers & Jeans</a></dd>
                              <dd><a href="index.php?id=64">Socks</a></dd>
                              <dd><a href="index.php?id=65">Underwear</a></dd>
                    </dl>
                    <dl>

                    </dl>
                </div>
            </li><!--menu end-->
                            <!--menu-->
                        <li><a href="index.php?id=8" class="blue">Boys</a>
                <div class="subs">
                    <dl>
                        <dd><a href="index.php?id=66">Coats & Jackets</a></dd>
                          <dd><a href="index.php?id=67">Jeans</a></dd>
                          <dd><a href="index.php?id=68">Joggers & Sweatshirts</a></dd>
                          <dd><a href="index.php?id=69">Jumpers & Cardigans</a></dd>
                          <dd><a href="index.php?id=70">Nightwear</a></dd>
                    </dl>
                    <dl>
                            <dd><a href="index.php?id=71">Shirts</a></dd>
                          <dd><a href="index.php?id=72">Shorts</a></dd>
                          <dd><a href="index.php?id=73">Sportswear</a></dd>
                          <dd><a href="index.php?id=74">Swimwear</a></dd>
                          <dd><a href="index.php?id=75">T-Shirts & Polo Shirts</a></dd>
                    </dl>
                    <dl>
                          <dd><a href="index.php?id=76">Trousers & Jeans</a></dd>
                          <dd><a href="index.php?id=77">Socks</a></dd>
                          <dd><a href="index.php?id=78">Underwear</a></dd>
                    </dl>
                    <dl>

                    </dl>
                </div>
            </li><!--menu end-->
            <!--menu-->
             <li><a href="index.php?id=9" class="blue">Toddlers</a>
                <div class="subs">
                    <dl>
                      <dd><a href="index.php?id=79">Newborn</a></dd>
                      <dd><a href="index.php?id=80">0-2 Years</a></dd>
                    </dl>                 
                </div>
            </li><!--menu end-->
            <!--menu-->
             <li><a href="index.php?id=10" class="blue">Accessories</a>
                <div class="subs">
                    <dl>
                          <dd><a href="index.php?id=81">Shoes</a></dd>
                          <dd><a href="index.php?id=82">Ties</a></dd>
                          <dd><a href="index.php?id=83">Caps</a></dd>
                          <dd><a href="index.php?id=84">Belts</a></dd>
                    </dl>                 
                </div>
            </li><!--menu end-->
            <li><a href="index.php?id=13" class="blue">Contact Us</a></li>
        </ul>
        <div class="back"></div>
        <div class="shadow"></div>
    </div>
    <div style="clear:both"></div>
</div>

Solution 3:

For a menu which responds to click events as opposed to just hover, and acts in a similar way to a select control...

ul, li {
    list-style:none;
    margin:0;
    padding:0;
}
li input {
    display:none;
}
ul:not(:focus) input:not(:checked), ul:not(:focus) input:not(:checked) + label {
    display:none;
}
input:checked+label {
    color:red;
}
<ul tabindex='0'>
    <li>
        <input id='item1' type='radio' name='item' checked='true' />
        <label for='item1'>Item 1</label>
    </li>
    <li>
        <input id='item2' type='radio' name='item' />
        <label for='item2'>Item 2</label>
    </li>
    <li>
        <input id='item3' type='radio' name='item' />
        <label for='item3'>Item 3</label>
    </li>
</ul>