{"rowid": 98, "title": "Absolute Columns", "contents": "CSS layouts have come quite a long way since the dark ages of web publishing, with all sorts of creative applications of floats, negative margins, and even background images employed in order to give us that most basic building block, the column. As the title implies, we are indeed going to be discussing columns today\u2014more to the point, a handy little application of absolute positioning that may be exactly what you\u2019ve been looking for\u2026\n\nCare for a nightcap?\n\nIf you\u2019ve been developing for the web for long enough, you may be familiar with this little children\u2019s fable, passed down from wizened Shaolin monks sitting atop the great Mt. Geocities: \u201cOnce upon a time, multiple columns of the same height could be easily created using TABLES.\u201d Now, though we\u2019re all comfortably seated on the standards train (and let\u2019s be honest: even if you like to think you\u2019ve fallen off, if you\u2019ve given up using tables for layout, rest assured your sleeper car is still reserved), this particular\u2014and as page layout goes, quite basic\u2014trick is still a thorn in our CSSides compared to the ease of achieving the same effect using said Tables of Evil\u2122.\n\nSee, the orange juice masks the flavor\u2026\n\nCreative solutions such as Dan Cederholm\u2019s Faux Columns do a good job of making it appear as though adjacent columns maintain equal height as content expands, using a background image to fill the space that the columns cannot.\n\nNow, the Holy Grail of CSS columns behaving exactly how they would as table cells\u2014or more to the point, as columns\u2014still eludes us (cough CSS3 Multi-column layout module cough), but sometimes you just need, for example, a secondary column (say, a sidebar) to match the height of a primary column, without involving the creation of images. This is where a little absolute positioning can save you time, while possibly giving your layout a little more flexibility.\n\nShaken, not stirred\n\nYou\u2019re probably familiar by now with the concept of Making the Absolute, Relative as set forth long ago by Doug Bowman, but let\u2019s quickly review just in case: an element set to position:absolute will position itself relative to its nearest ancestor set to position:relative, rather than the browser window (see Figure 1).\n\n Figure 1.\n\nHowever, what you may not know is that we can anchor more than two sides of an absolutely positioned element. Yes, that\u2019s right, all four sides (top, right, bottom, left) can be set, though in this example we\u2019re only going to require the services of three sides (see Figure 2 for the end result).\n\n Figure 2.\n\nTrust me, this will make you feel better\n\nOur requirements are essentially the same as the standard \u201cabsolute-relative\u201d trick\u2014a container
set to position:relative, and our sidebar
set to position:absolute \u2014 plus another
that will serve as our main content column. We\u2019ll also add a few other common layout elements (wrapper, header, and footer) so our example markup looks more like a real layout and less like a test case:\n\n
\n\t
\n\t\t

#header

\n\t
\n\t
\n\t\t
\n\t\t\t

#left

\n\t\t\t

Lorem ipsum dolor sit amet\u2026

\n\t\t
\n\t\t
\n\t\t\t

#right

\n\t\t
\n\t
\n\t
\n\t\t

#footer

\n\t
\n
\n\nIn this example, our main column (#column-left) is only being given a width to fit within the context of the layout, and is otherwise untouched (though we\u2019re using pixels here, this trick will of course work with fluid layouts as well), and our right keeping our styles nice and minimal:\n\n#container {\n\tposition: relative;\n}\n#column-left {\n\twidth: 480px;\n}\n#column-right {\n\tposition: absolute;\n\ttop: 10px;\n\tright: 10px;\n\tbottom: 10px;\n\twidth: 250px;\n}\n\nThe trick is a simple one: the #container
will expand vertically to fit the content within #column-left. By telling our sidebar
(#column-right) to attach itself not only to the top and right edges of #container, but also to the bottom, it too will expand and contract to match the height of the left column (duplicate the \u201clorem ipsum\u201d paragraph a few times to see it in action).\n\n Figure 3.\n\nOn the rocks\n\n\u201cBut wait!\u201d I hear you exclaim, \u201cwhen the right column has more content than the left column, it doesn\u2019t expand! My text runneth over!\u201d Sure enough, that\u2019s exactly what happens, and what\u2019s more, it\u2019s supposed to: Absolutely positioned elements do exactly what you tell them to do, and unfortunately aren\u2019t very good at thinking outside the box (get it? sigh\u2026). \n\nHowever, this needn\u2019t get your spirits down, because there\u2019s an easy way to address the issue: by adding overflow:auto to #column-right, a scrollbar will automatically appear if and when needed:\n\n#column-right {\n\tposition: absolute;\n\ttop: 10px;\n\tright: 10px;\n\tbottom: 10px;\n\twidth: 250px;\n\toverflow: auto;\n}\n\nWhile this may limit the trick\u2019s usefulness to situations where the primary column will almost always have more content than the secondary column\u2014or where the secondary column\u2019s content can scroll with wild abandon\u2014a little prior planning will make it easy to incorporate into your designs.\n\nDriving us to drink\n\nIt just wouldn\u2019t be right to have a friendly, festive holiday tutorial without inviting IE6, though in this particular instance there will be no shaming that old browser into admitting it has a problem, nor an intervention and subsequent 12-step program. That\u2019s right my friends, this tutorial has abstained from IE6-abuse now for 30 days, thanks to the wizard Dean Edwards and his amazingly talented IE7 Javascript library.\n\nSimply drop the Conditional Comment and