Adding scroll bar to dynamic ul li

Question

I searched through many posts and forum as i thought this might be a basic stuff but didnot find it so asking here,All i am trying to do is add scroll bar if the height is more than certain limit lets say if menu items are more than 3.

I have created a jsfiddle http://jsfiddle.net/euSWB/

If you are not able to access it then here is the HTML and CSS HTML

<ul id="mnav">

<li><a><b>Home</b></a>
</li>
<li><a><b>SQL Server vs Oracle</b></a>
 <ul>

<li><a>Basic SQL : Declare variables and assign values</a></li>

<li><a>Basic SQL : Inner Join, Outer Join and Cross Join</a></li>

<li><a>Basic SQL : Padding and Trimming</a></li>

<li><a>Basic SQL : Union,Except/Minus,Intersect</a></li>

<li><a style="border-bottom-color: currentColor; border-bottom-width: 0px; border-bottom-style: none;">Update from Select</a></li>

</ul>
</li>

<li><a href="#"><b>SSIS</b></a>
 <ul>
<li><a>Coalesce in SSIS</a></li>
<li><a >Universal CSV Generator</a></li>
<li><a >Parsing a row into multiple in CSV</a></li>


<li><a style="border-bottom-color: currentColor; border-bottom-width: 0px; border-bottom-style: none;" >XML Task in SSIS</a></li>
</ul>
 </li></ul>

CSS

#mnav {
margin-left: -30px;
margin-right: -30px;
}
#mnav li {
float: left;
list-style: none;
}
#mnav li a, #mnav li a:link, #mnav li a:visited {
text-decoration: none;
}
#mnav li a:hover, #mnav li a:active {
text-decoration: none;
}
#mnav li:hover, #mnav li.sfhover {
position: static;
}
#mnav li ul {
display: block;
z-index: 9999;
position: absolute;
left: -999em;
width: 400px;
margin: 0px;
border: 1px solid #ddd;
}
#mnav li:hover ul, #mnav li.sfhover ul {
left: auto;
}
#mnav li ul li a, #mnav li ul li a:link, #mnav li ul li a:visited {
display: block;
margin: 0;
text-decoration: none;
z-index: 9999;
border-bottom: 1px dotted #ccc;
width: 500px;
}
#mnav li ul li a:hover, #mnav li ul li a:active {
display: block;
margin: 0;
text-decoration: none;
}

Answer 1

I've made a couple of adjustments to your original stylesheet, and now it will show the scroll bar, but only when it exceeds the height of 3 list items (63 pixels in this case). Here's the final CSS code:

#mnav {
    margin-left: -30px;
    margin-right: -30px;
}
#mnav li {
    float: left;
    list-style: none;
    margin:0 10px;/*Keeping 10px space between each nav element*/
}
#mnav li a,/*These can all be merged into a single style*/
#mnav li a:link,
#mnav li a:visited,
#mnav li a:hover,
#mnav li a:active {
    text-decoration: none;
}
#mnav li ul {
    display: none;/*This is the default state.*/
    z-index: 9999;
    position: absolute;
    width: 400px;
    max-height:63px;/*The important part*/
    overflow-y:auto;/*Also...*/
    overflow-x:hidden;/*And the end of the important part*/
    margin: 0px;
    padding-left:5px;/*Removing the large whitespace to the left of list items*/
    border: 1px solid #ddd;
}
#mnav li:hover ul, #mnav li.sfhover ul {
    display:block;/*This is the hovered state*/
}
#mnav li ul li a, #mnav li ul li a:link, #mnav li ul li a:visited {
    display: block;
    margin: 0;
    text-decoration: none;
    z-index: 9999;
    border-bottom: 1px dotted #ccc;
    width:400px;
}
#mnav li ul li a:hover, #mnav li ul li a:active {
    display: block;
    margin: 0;
    text-decoration: none;
}

Here's the demo of it. I've also, for demonstration purposes, inserted 2 extra <li> elements to the Home and SQL Server vs Oracle items. The Home item will show how the popup behaves if there are fewer than 3 list items there.

To explain each of the changed bits, first the code that actually does the trick:

• defining the max-height to 63 will make the ul behave normally if it stays under 63px high, but if it exceeds that, it will overflow and show a scroll bar. If you want to show more items, just increase the max-height to the desired height. Currently the height of each item is 21px, so I used that to get the 63px for 3 items.
• Since the overflow should only show a scroll bar for the vertical direction, only overflow-y:auto; should be there, and overflow-x:hidden to prevent a scrollbar in the horizontal direction.

And then the other general changes I made:

• I've added 20px margin between items (10px on either side of the element) to make the list look a bit better here. You may want to apply your own style though, this is just for this demo.
• I've changed your hiding technique from 'shoving it off to -999em to the left' to hiding it via display:none. This is better to work with, since elements that are display:none will not render in search engines, so this will help in those situations. In general I think hiding things with display:none is just better than shoving it off the screen, while it's still actually there
• I've removed the padding to the left of the ul since it just looked quite bad. No need for the default padding if you're not using it for a dotted/numbered list.

This should also work considering your comment to Zachary Carter's answer, since this won't show a huge white box if you define the max-height to 210px (10 items).

Answer 2

If you have predictable list item heights, this is fairly trivial. Consider the following example:

<ul class="sub-menu">
    <li>This is option one.</li>
    <li>This is a second option.</li>
    <li>We'll need three.</li>
    <li>And now these are out of view.</li>
    <li>I'm the last option.</li>
</ul>

Here we have this list of five items. I will instruct each of the list items themselves to have a font-size and line-height of 1em, with a padding of .25em on the top and bottom:

.sub-menu li {
    font-size: 1em;
    padding: .25em 1em;
    line-height: 1em;
}

So now we know that each list item is 1.5em tall. As such, we can now set the max-height on our parent element so that it only shows three list items at a time:

.sub-menu {
    padding: 0;
    max-height: 4.5em; /* 1.5 x 3 */
    overflow-y: auto;
}

The results:

Online Demo: http://jsfiddle.net/euSWB/16/