Dec 07
CSS: The All-Expandable Box
by: Chris Coyier
In HTML, if you don’t specify a specific width, block-level elements are vertically expandable by their nature. Think of an unordered list. That list will grow be be as big as it needs to be to fit all of it’s list elements. If a user increases the font size in their browser, the list will expand vertically, growing to fit the larger content. Sometimes it feels like vertical-only expansion is limiting and it would be nice if the element could grow horizontally as well as vertically with a font size increase by the user.
Abstract
If you have been using the Firefox 3 beta much, you might notice that it handles this automatically. Increasing the size in Firefox 3 doesn’t just increase the font size, it increases everything in size, which actually feel really natural and nice. But despite it’s growing market share, we can’t count on Firefox for the resizing needs of our users.
I am going to attempt to explain how to make an All-Expandable box, with the following features:
- Works in all major browsers
- Expands both vertically and horizontally
- Uses a single background image
This is a bit of a tall order, especially the use of the background image. This will end up using kind of a combination of the CSS sprites technique since different areas of the image will be used in different places and the Sliding Doors technique, since different amounts of those images will be visible depending on the current size.
Make the box horizontally expandable
There is one way simple way to make a box horizontally expandable: specify your width in em’s. For example:
.box {
width: 35em;
margin: 50px auto;
}The margin is there for example purposes, to keep it centered and away from the top edge of the browser window.
Thinking about image placement
In this example, the box has rounded corners, a bit of a drop shadow, and a bit of an inner shadow. This means that all of the four corners of the box are distinctly different. This is uniquely challenging since images are not expandable. We will need a way to apply the four different corner images to the four corners of the box separately.
Also, we will need to overlap them in such a way that the transitions are seamless. And also, we are trying to do this with only a single background image, to make it as efficient as possible.
Below is an image of how you might think of what we need to do. The boxes would be overlapping, I nudged them apart so you can see the whole boxes.
When creating the background image, think big. The bigger your background image, the larger you will be able to expand without borking the layout. The example background is 700px wide which gets you about 4 or 5 different text sizings it works at, but it does eventually break apart above that.
Coding the box
Of course we always like to be as semantic as possible with our XTHML. That means not using extra markup for things that aren’t really content but are purely design. Unfortunately, with all this craziness of needing four boxes for our single box, it ain’t gonna happen.
This is how it’s done:
<div class="box">
<div class="topleft">
<div class="topright">
<div>
CONTENT GOES HERE
</div>
</div>
</div>
<div class="bottomleft">
<div class="bottomright">
</div>
</div>
</div>
Styling the box
Here is the CSS for the four areas within the box:
.box div.topleft {
display: block;
background: url("images/box-bg.png") top left no-repeat white;
padding: 2.0em 0em 0em 2.0em;
}
.box div.topright {
display: block;
background: url("images/box-bg.png") top right no-repeat white;
padding: 2.0em;
margin: -2.0em 0 0 2.0em;
}
.box div.bottomleft {
display: block;
height: 45px;
margin-top: -2.0em;
background: url("images/box-bg.png") bottom left no-repeat white;
}
.box div.bottomright {
display: block;
background: url("images/box-bg.png") bottom right no-repeat white;
height: 45px;
margin-left: 3.0em;
}
Note the negative margins are necessary to pull back from the padding applied from the parent spans. It just works out good that way with the padding, keeping text inside the box. Also note the height of the bottom spans are set in pixels. That is on purpose as they need to be kept short and not be expandable.
This has been tested in Firefox, Safari, Opera, and IE 6 and is working in all of them, so I’m fairly satisfed it’s a solid technique.
Credits
This tutorial is contributed by Chris Coyier. Visit CSS-Tricks to learn more CSS tricks from Chris.
Update:
The code in this example was updated to fix the div within a span issue and now validates.
Best of CSS Design 2007 Typographic Contrast and Flow
Comments
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There are 110 comments (+Add)
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110 Dave
February 24th, 2010 at 4:51 pm
Great, but why does the background box on THIS page stops halfway through the text and never gets close to the bottom of the page? Oh, and the comments don’t seem to fit in the comments boxes if over 2 lines. Viewed with IE8 btw. Nice to find free css tuts though. Thanks
109 jams
February 23rd, 2010 at 10:55 am
Nice Tutor….
108 Oliver http://www.electricflare.net
February 17th, 2010 at 6:43 am
nice trick. I don’t think it matters about lack of IE6 support, considering recent revelations of IE6 being a security issue. The more we continue to support this old browser the longer it will take to disappear for good.
107 Tzon Tikis
February 16th, 2010 at 3:55 am
It doesn’t work on IE6
106 Faraz http://www.farazhameedkhan.co.cc
February 12th, 2010 at 12:30 am
Nice CSS!
105 Vertex Web Solutions http://www.vertexwebspace.com
February 3rd, 2010 at 7:03 am
Great , CSS Thanks for Shear
104 Waqas http://www.ahcorporation.com
January 15th, 2010 at 7:56 am
Kindly check it on IE 6.0, there is some bug with expandable box.
anyway Nice trick!
103 w
January 12th, 2010 at 9:52 pm
Very nice box! Except for the nasty blurred edges. ick….
102 vincentdresses http://www.hibridal.com
January 5th, 2010 at 11:32 pm
The designs showed here show what simple and tasteful design is all about. Another one to consider
101 kinza http://www.designerpk.com
November 30th, 2009 at 10:23 pm
hey
this is great post you have save my time keep it up thanks for sharing.
kinza