By: Trenton Moss

January 20th, 2005

Reader Rating: 9

More and more Web developers are ditching tables and coming round to the idea of using CSS to control the layouts of sites. And, given the many benefits of using CSS, such as quicker download time, improved accessibility and easier site management, why not?

The Problem with CSS

Historically, the main problem with using CSS has been a lack of browser support. This is no longer the case, as version 5 browsers, which all provide good support for CSS, now account for over 99% of the browsers in use.

The problem that remains is that browsers can sometimes interpret CSS commands in different ways, which fact alone causes many developers to throw their arms up in the air and switch back to pixel-perfect table layouts. Fear not, though! As you learn more about CSS, you'll gradually start to understand the different browser interpretations and realise that there aren't really that many -- and that, where necessary, their idiosyncrasies can be catered to using various workarounds or hacks.

How CSS Hacks Work

The way CSS hacks works is to send one CSS rule to the browser(s) you're trying to trick, and a second CSS rule that overrides the first command to the other browsers. If you have two CSS rules with identical selectors, the second CSS rule will almost always take precedence.

Say, for example, you want the space between a page's header area and its content to total 25px in Internet Explorer. This gap might look good in IE, but in Firefox, Opera and Safari the gap is huge -- you decide that a 10px gap looks far better. To achieve this perfect look in all browsers, you could use the following two CSS rules:

#header {margin-bottom:25px}
#header {margin-bottom:10px}

The first command is intended for IE, the second for all other browsers. How does this work? Well, it won't at the moment because all browsers can understand both CSS rules. As such, they'll all use the second CSS rule because it comes after the first.

By inserting a CSS hack, we can perform browser detection by hiding the second CSS rule from IE. This means that IE won't even know that rule exists, and will therefore use the first CSS rule. How do we do this? Read on to find out!

Browser Detection for Internet Explorer

To send different CSS rules to IE, we can use the child selector command, which IE can't understand. The child selector command involves two elements, one of which is the child of the other. So, html>body refers to the child, body, contained within the parent, html.

Using the example of the header margin, our CSS command would be:

#header {margin-bottom:3em}
html>body #header {margin-bottom:1em}

IE can't understand the second CSS rule, due to the html>body CSS command, so it will ignore it and use the first rule. All other browsers will use the second rule.

Browser Detection for Internet Explorer 5

It may seem strange at first to send different CSS rules to different versions of a browser, but in the case of IE5 it's very necessary. The problem lies in IE5's misinterpretation of the box model. When we specify the width of an element in CSS, padding and borders aren't included in this value. IE5, however, incorporates these values into the width value, which causes element widths to become smaller in this browser.

The following CSS rule would result in a width of 10em for all browsers, except IE5, which would give it a width of just 5em (IE5 would incorporate two sets of padding and border, on both the left and right, when calculating the width):

#header {padding: 2em; border: 0.5em; width: 10em}

The solution to this problem? The box model hack [1], invented by Tantek Çelik, who has become quite famous in the CSS world as a result of this hack -- and rightly so. To perform browser detection, and send a different CSS rule to IE5 you would use the following:

#header {padding: 2em; border: 0.5em; width: 15em; voice-family: "\"}\""; voice-family:inherit; width: 10em}

How Mr. Celik worked out how to do this is anyone's guess! The important thing is that it works: IE5 will use the first width value of 15em, 5em of which will be taken up by the two sets of padding and border (one each for the left and for the right). This would ultimately give the element a width of 10em in IE5.

The 15em value will then be overridden by the second width value of 10em by all browsers except IE5, which, for some reason, can't understand the CSS command that comes immediately after all those squiggles. It doesn't look pretty, but it does work!

There is a slight problem with the box model hack, as it can often 'kill' the next CSS rule in IE5.0. However, there are plenty of other box model hacks [2] that you could implement instead.

Browser Detection for Internet Explorer on the Mac

Quite simply, IE on the Mac does strange things with CSS. The browser's become somewhat obsolete since Microsoft announced it's not going to release an updated version. As such, many Web developers code their CSS-driven sites so that the site works in IE/Mac, although it may not offer the same level of advanced functionality or design that's offered to users of other platform and browser combinations. Provided IE/Mac users can access all areas of the site, this is seen as a suitable way to do things.

To hide a command using the IE/Mac CSS hack [3] is simple. It involves wrapping a set of dashes and stars around as many CSS rules as you like:

/* Hide from IE-Mac \*/
#header {margin-bottom:3em}
#footer {margin-top:1.5em}
/* End hide */

IE/Mac will simply ignore all these commands. This CSS hack can actually be quite useful if there's a certain area of the site that doesn't work properly in IE/Mac. If that section isn't fundamental to visitors' use of the site, you can simply hide it from IE/Mac like so:

#noiemac {display: none}

/* Hide from IE-Mac \*/
#noiemac {display: block}
/* End hide */

The first CSS rule hides the entire section assigned the noiemac id (i.e. <div id="noiemac">). The second CSS rule, which IE/Mac can't see, displays this section.

Browser Detection for Netscape 4

Netscape 4 has limited and somewhat erratic support for CSS. Making a CSS layout for this browser, whose market share has now slipped well below 1%, can be extremely challenging. It's become common practice nowadays to completely hide the CSS file from this browser. This can be achieved using the @import directive to call up the CSS document:

<style type="text/css">@import url(cssfile.css);</style>

Netscape 4 will display a non-styled version of the site, as it can't understand this @import directive.

Checking your Site in the Different Browsers

At the time of writing, the major Internet browsers include IE5, IE6, Firefox, Opera and Safari. (Check out TheCounter.com [4] for up-to-date browser statistics.) You can download all these browsers, and a number of more obscure ones, at the Evolt browser archive [5]. If you're not sure how, find out how to install multiple versions of IE on your PC [6].

Ideally, you should check your site in all these browsers, on both PC and Mac (except IE6 and Safari, which are only available on PC and Mac respectively). If you don't have access to a Mac you can get a screenshot of your site on Safari by running it through Dan Vine's iCapture [7], or you can pay to use Browsercam [8], which offers a more extensive screen capturing service.

Conclusion

On the whole, modern browsers have very good support for CSS -- it's certainly good enough for you to use CSS to control layout and presentation. Sometimes however, certain page elements will appear differently in different browsers.

Don't worry too much if you don't know the reason why: play around with the CSS rules and make some trial-and-error changes, such as perhaps changing a padding value to a margin. If that doesn't work, you can fix it up with these CSS hacks and your Web pages should look great across all browsers!

[1] http://tantek.com/CSS/Examples/boxmodelhack.html
[2] http://css-discuss.incutio.com/?page=BoxModelHack
[3] http://www.sam-i-am.com/work/sandbox/css/mac_ie5_hack.html
[4] http://www.thecounter.com/stats/
[5] http://browsers.evolt.org/
[6] http://labs.insert-title.com/labs/article.aspx?ID=795
[7] http://www.danvine.com/icapture/
[8] http://www.browsercam.com/