wordpress dropdown menu

***If we want to use dropdown menu then we have to thinking about below…
1.  Z-index
2.  Don’t use overflow:hidden

// html code
<div id='cssmenu'>
<ul>
   <li><a href='#'><span>Home</span></a></li>
   <li class='active has-sub'><a href='#'><span>Products</span></a>
      <ul>
         <li class='has-sub'><a href='#'><span>Product 1</span></a>
            <ul>
               <li><a href='#'><span>Sub Product</span></a></li>
               <li class='last'><a href='#'><span>Sub Product</span></a></li>
            </ul>
         </li>
         <li class='has-sub'><a href='#'><span>Product 2</span></a>
            <ul>
               <li><a href='#'><span>Sub Product</span></a></li>
               <li class='last'><a href='#'><span>Sub Product</span></a></li>
            </ul>
         </li>
      </ul>
   </li>
   <li><a href='#'><span>About</span></a></li>
   <li class='last'><a href='#'><span>Contact</span></a></li>
</ul>

// CSS code
@import url(http://fonts.googleapis.com/css?family=Oxygen+Mono);
/* Starter CSS for Menu */
#cssmenu {
  padding: 0;
  margin: 0;
  border: 0;
  width: auto;
}
#cssmenu ul,
#cssmenu li {
  list-style: none;
  margin: 0;
  padding: 0;
}
#cssmenu ul {
  position: relative;
  z-index: 597;
}
#cssmenu ul li {
  float: left;
  min-height: 1px;
  vertical-align: middle;
}
#cssmenu ul li.hover,
#cssmenu ul li:hover {
  position: relative;
  z-index: 599;
  cursor: default;
}
#cssmenu ul ul {
  visibility: hidden;
  position: absolute;
  top: 100%;
  left: 0;
  z-index: 598;
  width: 100%;
}
#cssmenu ul ul li {
  float: none;
}
#cssmenu ul ul ul {
  top: 0;
  left: 190px;
  width: 190px;
}
#cssmenu ul li:hover > ul {
  visibility: visible;
}
#cssmenu ul ul {
  bottom: 0;
  left: 0;
}
#cssmenu ul ul {
  margin-top: 0;
}
#cssmenu ul ul li {
  font-weight: normal;
}
#cssmenu a {
  display: block;
  line-height: 1em;
  text-decoration: none;
}
/* Custom CSS Styles */
#cssmenu {
  background: #333333;
  border-bottom: 4px solid #1b9bff;
  font-family: 'Oxygen Mono', Tahoma, Arial, sans-serif;
  font-size: 12px;
}
#cssmenu > ul {
  *display: inline-block;
}
#cssmenu:after,
#cssmenu ul:after {
  content: '';
  display: block;
  clear: both;
}
#cssmenu ul {
  text-transform: uppercase;
}
#cssmenu ul ul {
  border-top: 4px solid #1b9bff;
  text-transform: none;
  min-width: 190px;
}
#cssmenu ul ul a {
  background: #1b9bff;
  color: #ffffff;
  border: 1px solid #0082e7;
  border-top: 0 none;
  line-height: 150%;
  padding: 16px 20px;
  font-size: 12px;
}
#cssmenu ul ul ul {
  border-top: 0 none;
}
#cssmenu ul ul li {
  position: relative;
}
#cssmenu ul ul li:first-child > a {
  border-top: 1px solid #0082e7;
}
#cssmenu ul ul li:hover > a {
  background: #4eb1ff;
  color: #ffffff;
}
#cssmenu ul ul li:last-child > a {
  -moz-border-radius: 0 0 3px 3px;
  -webkit-border-radius: 0 0 3px 3px;
  border-radius: 0 0 3px 3px;
  -moz-background-clip: padding;
  -webkit-background-clip: padding-box;
  background-clip: padding-box;
  -moz-box-shadow: 0 1px 0 #1b9bff;
  -webkit-box-shadow: 0 1px 0 #1b9bff;
  box-shadow: 0 1px 0 #1b9bff;
}
#cssmenu ul ul li:last-child:hover > a {
  -moz-border-radius: 0 0 0 3px;
  -webkit-border-radius: 0 0 0 3px;
  border-radius: 0 0 0 3px;
  -moz-background-clip: padding;
  -webkit-background-clip: padding-box;
  background-clip: padding-box;
}
#cssmenu ul ul li.has-sub > a:after {
  content: '+';
  position: absolute;
  top: 50%;
  right: 15px;
  margin-top: -8px;
}
#cssmenu ul li:hover > a,
#cssmenu ul li.active > a {
  background: #1b9bff;
  color: #ffffff;
}
#cssmenu ul li.has-sub > a:after {
  content: '+';
  margin-left: 5px;
}
#cssmenu ul li.last ul {
  left: auto;
  right: 0;
}
#cssmenu ul li.last ul ul {
  left: auto;
  right: 99.5%;
}
#cssmenu a {
  background: #333333;
  color: #CBCBCB;
  padding: 0 20px;
}
#cssmenu > ul > li > a {
  line-height: 48px;
  font-size: 12px;
}

// use in functions.php
// add menu support and fallback menu if menu doesn't exist
    add_action('init', 'wpj_register_menu');
    function wpj_register_menu() {
        if (function_exists('register_nav_menu')) {
            register_nav_menu( 'wpj-main-menu', __( 'Main Menu', 'brightpage' ) );
        }
    }
    function wpj_default_menu() {
        echo '<ul id="dropmenu">';
        if ('page' != get_option('show_on_front')) {
            echo '<li><a href="'. home_url() . '/">Home</a></li>';
        }
        wp_list_pages('title_li=');
        echo '</ul>';
    }

// use your menu area where  there is menu
<div  id='cssmenu' class=" floatright">
                <?php
                if (function_exists('wp_nav_menu')) {
                    wp_nav_menu(array('theme_location' => 'wpj-main-menu', 'menu_id' => 'dropmenu', 'fallback_cb' => 'wpj_default_menu'));
                }
                else {
                    wpj_default_menu();
                }
                ?>
            </div>