Why does layout change in IE when UL is alone in a TD vs having an extra empty DIV?

StackOverflow https://stackoverflow.com/questions/1212860

Question

I'm adding css-based tab navigation to a site that is still using table-based layout. When I place my tab list inside a td, there is a visual "gap" that you can see. If I put an empty div with width: 100% in the td, then my tab list displays correctly. (It also works fine outside the table.)

Why does the div make the tabs lay out correctly, and is there a better way to make them do so without adding a content-free div?

Here's my test case:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" >
    <head><title>
    Strange gap
</title>
   <style type ="text/css" >
/* stolen from http://unraveled.com/publications/css_tabs/, then hacked to death */

ul.tabnav { /* general settings */
border-bottom: 1px solid #cbcbcd; /* set border COLOR as desired */
list-style-type: none;
padding: 3px 10px 3px 10px; /* THIRD number must change with respect to padding-top (X) below */
margin: 3px 0px 0px 0px; /* Right on top of the next row */
}

ul.tabnav li { /* do not change */
display: inline;
}

ul.tabnav li.current { /* settings for selected tab */
border-bottom: 1px solid #fff; /* set border color to page background color */
background-color: #fff; /* set background color to match above border color */
/* border: solid 1px red; */
}

ul.tabnav li.current a { /* settings for selected tab link */
background-color: #fff; /* set selected tab background color as desired */
color: #000; /* set selected tab link color as desired */
position: relative;
top: 1px;
padding-top: 4px; /* must change with respect to padding (X) above and below */
}

ul.tabnav li a { /* settings for all tab links */
padding: 3px 4px; /* set padding (tab size) as desired; FIRST number must change with respect to padding-top (X) above */
border: 1px solid #cbcbcd; /* set border COLOR as desired; usually matches border color specified in #tabnav */
background-color: #cbcbcd; /* set unselected tab background color as desired */
color: #666; /* set unselected tab link color as desired */
margin-right: 0px; /* set additional spacing between tabs as desired */
text-decoration: none;
border-bottom: none;
}

/* end css tabs */
    </style>         
    </head>
    <body>

            <table>
                <tr>
                    <td>
                    I'm making some tab navigation with css. I copied the code 
                    from <a href=" http://unraveled.com/publications/css_tabs/"> http://unraveled.com/publications/css_tabs/</a>,
                    and hacked it up. There's an odd behavior that I see on IE (v 7).
                    There's a gap below.

                    </td>
                </tr>
                <tr>
                <td>
                        <ul class="tabnav">
                            <li class="current"><a >Home</a></li>
                            <li ><a >Search</a></li>
                        </ul>
                </td>
                </tr>
                <tr>
                    <td>

                    No gap below this

                    </td>
                </tr>
                <tr>
                <td  >
                <div style="width: 100%"><!-- This div forces the menu to render properly in IE7. I don't know why --></div>
                        <ul class="tabnav">
                            <li class="current"><a >Home</a></li>
                            <li ><a>Search</a></li>
                        </ul>
                </td>
                </tr>
                <tr>
                    <td>

                    why? The difference is the presence of a div with style="width: 100%" on it in the second 
                    case. I don't know why this fixes the rendering; I'd like a better way to do it without adding an 
                    extra empty div. This page should be in standards mode (or at least non-quirks mode).

                    </td>
                </tr>
            </table>

            For comparison, it works fine outside of a table:

                        <ul class="tabnav">
                            <li class="current"><a >Home</a></li>
                            <li ><a >Search</a></li>
                        </ul>

    </body>
</html>

I've now crossposted this to my blog: Bacon Driven Coding: Why does layout change in IE when UL is alone in a TD vs having an extra empty DIV?, with a screenshot so people can see what I'm talking about.

Here's the screenshot:

Mind the Gap

Was it helpful?

Solution

The gap is caused by IE's funny ways with lists. Since ul tags can only contain <li>s, IE apparently also believes the whitespace between the list items is inappropriate and moves it inside the preceding list item, in your case following the <a>.

That then causes the white background of the selected tab to overlap the <ul>s bottom border (due to its positioning).

It looks like the easiest way to solve it in this example is simply to remove the background color on ul.tabnav li.current. In fact, I think you can remove that entire ruleset, since the border doesn't do anything either.

If none of that helps you fix it on the actual site, a last resort could be to get rid of all whitespace outside the <li> tags. E.g.

<ul><li><a>Home</a></li><li>etc.</li></ul>

or something like this if you want to retain some semblance of formatting:

   <ul><!--
   --><li><a>Home</a></li><!--
   --><li>etc.</li><!--
   --></ul>

But that whitespace is also all that's responsible for the spacing between the tabs, so you'd have to add a right margin to bring it back.

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