Try it Editor -

<!Doctype html>
<html>
<body>
<style>
#nav {
list-style:none inside;
margin:0;
padding:0;
text-align:center;
}
#nav li {
display:block;
position:relative;
float:left;
background: #24af15; /* menu background color */
}
#nav li a {
display:block;
padding:0;
text-decoration:none;
width:200px; /* this is the width of the menu items */
line-height:35px; /* this is the hieght of the menu items */
color:#ffffff; /* list item font color */
}
#nav li li a {font-size:80%;} /* smaller font size for sub menu items */
#nav li:hover {background:#003f20;} /* highlights current hovered list item and the parent list items when hovering over sub menues */
#nav ul {
position:absolute;
padding:0;
left:0;
display:none; /* hides sublists */
}
#nav li:hover ul ul {display:none;} /* hides sub-sublists */
#nav li:hover ul {display:block;} /* shows sublist on hover */
#nav li li:hover ul {
display:block; /* shows sub-sublist on hover */
margin-left:200px; /* this should be the same width as the parent list item */
margin-top:-35px; /* aligns top of sub menu with top of list item */
}
</style>
</head>
<ul id="nav">
<li><a href="#">Main Item 1</a></li>
<li><a href="#">Main Item 2</a>
<ul>
<li><a href="#">Sub Item</a></li>
<li><a href="#">Sub Item</a></li>
<li><a href="#">SUB SUB LIST »</a>
<ul>
<li><a href="#">Sub Sub Item 1</a>
<li><a href="#">Sub Sub Item 2</a>
</ul>
</li>
</ul>
</li>
<li><a href="#">Main Item 3</a></li>
</ul>
</body>
</html>