Bruce Lawson recently asked for ways to style a definition list in the common glossary format. This is one way to do it.

Bruce’s original post – css challenge – describes what he is after: a “glossary style” appearance with the term on the left and the definitions on the right. Some terms will have multiple definitions, definitions of varying length, and each new term should appear on a new line. A definition list is semantically correct for this kind of information, so there was to be no fiddling around with the HTML, and the browser requirements were for it to work in all modern browsers and IE 6+.

You can skip straight to the demo where some additional classes are included in the HTML in order to highlight each term-definition association.

The basic HTML

The basic HTML structure is a simple definition list and nothing more. There are some short, long, and multiple definitions for each term.

<h1>Styling definition lists</h1>
<dl>
  <dt>Cheese</dt>
  <dd>
    <p>Velit esse cillum dolore in reprehenderit in voluptate duis aute irure dolor. Consectetur adipisicing elit, excepteur sint occaecat sunt in culpa. Velit esse cillum dolore eu fugiat nulla pariatur. Ut aliquip ex ea commodo consequat.</p>
    <p>Mollit anim id est laborum. Ut enim ad minim veniam, consectetur adipisicing elit, ullamco laboris nisi. Lorem ipsum dolor sit amet, sunt in culpa quis nostrud exercitation.</p>
  </dd>
  <dd>yummy!</dd>

  <dt>Building flexibility through spreading knowledge and self-organization, exploiting the productive lifecycle to experience a profound paradigm shift. Through the adoption of a proactive stance, the astute manager can adopt a position at the vanguard.</dt>
  <dd>balderdash</dd>;
  <dd>poppycock</dd>

  <dt>Aardvark</dt>
  <dd>never hurt anyone</dd>
</dl>

The styles

In order to get the required appearance in all browsers I had to use negative margins and a few conditional styles to get IE7 and IE6 to play along.

For the purposes of the demo I’ve placed all the styles in <style> blocks in the head of the document.

<style>
   dl {padding-left:300px;}
   dt {clear:both; float:left; width:260px; padding:10px; margin:0 0 2em -300px; font-weight:bold; color:#686663;}
   dd {float:left; width:100%; padding:10px 0; margin:0 0 2em;}
</styl>
<!--[if lte IE 7]>
<style>
   dt {display:inline; margin-bottom:0;}
   dd {float:none; width:auto;}
</style>
<![endif]-->

That’s it. The widths of the <dt> can be set in ems or percentages if the layout requires. The complete code is available in the demo and you are free to use this code.

Over the weekend two new HTML5 elements – summary and figcaption – were added to the draft specification. The introduction of summary and figcaption marks the acceptance that new elements are needed to act as captions or legends for the details and figure elements. The addition of the figcaption element finally begins to clear up the difficulty in marking-up figure element captions and looks to cement the place of the figure element in the HTML5 specification. The summary element does much the same for the details element but the very nature of the details element itself means that its future is not yet clear.

The figcaption element

This new element acts as the optional caption or legend for any content contained within its parent figure element.

If there is no figcaption element within a figure element then there is no caption for the rest of its content. If there is a figcaption element then it must be the first or last child of the figure element and only the first figcaption element (should there be more than one child figcaption of the parent figure element) represents a caption.

The figure element is used to mark up any self-contained content that may be referenced from the main flow of a document but could also be removed from the primary content (for example, to an appendix) without affecting its flow. This makes it suitable for various types of content ranging from graphs and data tables to photographs and code blocks.

<p><a href="#fig-ftse">Figure 1</a> shows the extent of the collapse in the markets and how recovery has been slow.</p>

<figure id="fig-ftse">
  <figcaption>Figure 1. The value of the FTSE 100 Index from 1999&ndash;2009.</figcaption>
  <img src="ftse-100-index-graph.jpg" alt="The index hit a record high at the end of 1999 and experienced two significant drops in the following last decade.">
</figure>

<p>This latest financial crisis hasn't stopped Alex from writing music and his latest track is actually worth listening to.</p>

<figure>
  <audio src="what-am-i-doing.mp3" controls></audio>
  <figcaption><cite>What am I doing?</cite> by Alex Brown</figcaption>
</figure>

The creation of the figcaption element is an important step forward for the HTML5 draft specification as it finally provides a reliable means to markup the caption for content that is best marked up as a figure. Previous attempts to use the legend element, the caption element, and the dt and dd elements had failed due to a lack of backwards compatibility when it came to styling these elements with CSS.

The summary element

This new element represents a summary, caption, or legend for any content contained within its parent details element.

The summary element must be the first child of a details element and if there is no summary element present then the user agent should provide its own. The reason for this is because the details element has a specific function – to markup additional information and allow the user to toggle the visibility of the additional information. Although it is not specified in the specification, it is expected that the summary element will act as the control that toggles the open-closed status of the contents of the parent details element.

<details>
  <summary>Technical details.</summary>
  <dl>
    <dt>Bit rate:</dt> <dd>190KB/s</dd>
    <dt>Filename:</dt> <dd>drum-and-bass-mix.mp3</dd>
    <dt>Duration:</dt> <dd>01:02:34</dd>
    <dt>File size:</dt> <dd>78.9MB</dd>
  </dl>
</details>

The introduction of the summary element seems to secure the future of the details element and the new behaviour that it affords, for now. When user agents begin to add support for the details element you won’t need JavaScript, or even CSS, to have expanding or collapsing sections in an HTML document.

The future of the details element

There will continue to be some debate over the inclusion of behaviour in an HTML specification especially given the widespread use of JavaScript to provide the expand-collapse functionality that details describes.

The details element writes some quite significant behaviour into an HTML document and I can see it being abused to provide generic expand-collapse functionality throughout a document. It is also not entirely clear what purpose the details element actually serves other than being an attempt to bypass the need for JavaScript or CSS to expand or collapse sections of a document.

There has been a general softening of the rough distinction between content, presentation, and behaviour. JavaScript libraries are being used to patch holes in browser CSS and HTML5 support, the CSS3 modules introduce plenty of behaviour that was previously only possibly with JavaScript, and the HTML5 specification is also introducing functionality and behaviour that previously required the use of JavaScript.

The future survival of the details element, and the behaviour associated with it, may well depend on browser implementations and author applications over the coming months.

Using within-page links presses the jumped-to content right at the very top of the viewport. This can be a problem when using a fixed header. With a bit of hackery, there are some CSS methods to insert space between the top of the viewport and the target element within a page.

Demo: Jump links and viewport positioning

Known support: varies depending on method used.

This experiment is the result of a post Chris Coyier made on Forrst. Chris’ method was to add an empty span element to the target element, shift the id attribute onto the span, and then absolutely position the span somewhere above it’s parent element.

That method works but it requires changes to the HTML. The comments on Chris’ post suggested the use of psuedo-elements or padding. This experiment expands on, and combines, some of those suggestions to show the limitations of each method and document their browser support.

Simplest method

If you need to jump to an element with simple styling then using the :before pseudo-element is a quick and simple approach.

#target:before {
   content: "";
   display: block;
   height: 50px;
   margin: -30px 0 0;
}

The drawbacks are that it requires browser support for pseudo-elements and it will fail if the target element has a background colour, a repeated background image, padding-top, or border-top as part of its rule set.

More robust method

The more robust method uses a transparent border, negative margin, and the background-clip property. If a top border is required then it can be mimicked using a pseudo-element, as described in Multiple Backgrounds and Borders with CSS 2.1.

#target {
   position: relative;
   border-top: 52px solid transparent;
   margin: -30px 0 0;
   -webkit-background-clip: padding-box;
   -moz-background-clip: padding;
   background-clip: padding-box;
}

#target:before {
   content: "";
   position: absolute;
   top: -2px;
   left: 0;
   right: 0;
   border-top: 2px solid #ccc;
}

There are still drawbacks: it requires browser support for background-clip if there is a background color, gradient, or repeating image set on the target element; it requires browser support for pseudo-elements and their positioning if a top border is desired; and it interferes with the standard use of margins.

To see these methods in action – as well as more details on the code, browser support, and drawbacks – have a look at the demo page. Please let me know if you know of better techniques.

Research into improving the cross-browser consistency of both the “clearfix” and “overflow:hidden” methods of containing floats. The aim is to work around several bugs in IE6 and IE7.

This article introduces a new hack (with caveats) that can benefit the “clearfix” methods and the new block formatting context (NBFC) methods (e.g. using overflow:hidden) of containing floats. It’s one outcome of a collaboration between Nicolas Gallagher (that’s me) and Jonathan Neal.

If you are not familiar with the history and underlying principles behind methods of containing floats, I recommend that you have a read of Easy clearing (2004), Everything you know about clearfix is wrong (2010), and Clearfix reloaded and overflow:hidden demystified (2010).

Consistent float containment methods

The code is show below and documented in this GitHub gist. Found an improvement or flaw? Please fork the gist or leave a comment.

Micro clearfix hack: Firefox 3.5+, Safari 4+, Chrome, Opera 9+, IE 6+

.cf {
  /* for IE 6/7 */
  *zoom: expression(this.runtimeStyle.zoom="1", this.appendChild(document.createElement("br")).style.cssText="clear:both;font:0/0 serif");
  /* non-JS fallback */
  *zoom: 1;
}

.cf:before,
.cf:after {
  content: "";
  display: table;
}

.cf:after {
  clear: both;
}

Overflow hack (NBFC): Firefox 2+, Safari 2+, Chrome, Opera 9+, IE 6+

.nbfc {
  overflow: hidden;
  /* for IE 6/7 */
  *zoom: expression(this.runtimeStyle.zoom="1", this.appendChild(document.createElement("br")).style.cssText="clear:both;font:0/0 serif");
  /* non-JS fallback */
  *zoom: 1;
}

The GitHub gist also contains another variant of the clearfix method for modern browsers (based on Thierry Koblentz’s work). It provides greater visual consistency (avoiding edge-case bugs) for even older versions of Firefox.

The only difference from existing float-containment methods is the inclusion of a CSS expression that inserts a clearing line-break in IE 6 and IE 7. Jonathan and I found that it helps to resolve some of the visual rendering differences that exist between these browsers and more modern ones. First I’ll explain what some of those differences are and when they occur.

Containing floats in IE 6/7

In IE 6 and IE 7, the most common and robust method of containing floats within an element is to give it “layout” (find out more: On having Layout). Triggering “layout” on an element in IE 6/7 creates a new block formatting context (NBFC). However, certain IE bugs mean that previous float containment methods don’t result in cross-browser consistency. Specifically, this is what to expect in IE 6/7 when creating a NBFC:

1. The top- and bottom-margins of non-floated child elements are contained within the ancestor element that has been given “layout”. (Also expected in other browsers when creating a NBFC)
2. The bottom-margins of any right-floated descendants are contained within the ancestor. (Also expected in other browsers when creating a NBFC)
3. The bottom-margins of any left-floated children are not contained within the ancestor. The margin has no effect on the height of the ancestor and is truncated, having no affect outside of the ancestor either. (IE 6/7 bug)
4. In IE 6, if the right edge of the margin-box of a left-floated child is within 2px of the left edge of the content-box of its NBFC ancestor, the float’s bottom margin reappears and is contained within the parent. (IE 6 bug)
5. Unwanted white-space can appear at the bottom of a float-container. (IE 6/7 bug)

There is a lack of consistency between IE 6/7 and other browsers, and between IE 6 and IE 7. Thanks to Matthew Lein for his comment that directed me to this IE 6/7 behaviour. It was also recently mentioned by “Suzy” in a comment on Perishable Press.

IE 6/7’s truncation of the bottom-margin of left-floats is not exposed in many of the test-cases used to demonstrate CSS float containment techniques. Using an IE-only CSS expression helps to correct this bug.

The CSS expression

Including the much maligned <br style="clear:both"> at the bottom of the float-container, as well as creating a NBFC, resolved all these inconsistencies in IE 6/7. Doing so prevents those browsers from collapsing (or truncating) top- and bottom-margins of descendant elements.

Jonathan suggested inserting the clearing line-break in IE 6/7 only, using CSS expressions applied to fictional CSS properties. The CSS expression is the result of many iterations, tests, and suggestions. It runs only once, the first time an element receives the associated classname.

*zoom: expression(this.runtimeStyle.zoom="1", this.appendChild(document.createElement("br")).style.cssText="clear:both;font:0/0 serif");

It is applied to zoom, which is already being used to help contain floats in IE 6/7, and the use of the runtimeStyle object ensures that the expression is replaced once it has been run. The addition of font:0/0 serif prevents the occasional appearance of white-space at the bottom of a float-container. And the * hack ensures that only IE 6 and IE 7 parse the rule.

It’s worth noting that IE 6 and IE 7 parse almost any string used as CSS property. An earlier iteration used the entirely fictitious properties “-ms-inject” or “-ie-x” property to exploit this IE behaviour.

*-ie-x: expression(this.x||(this.innerHTML+='<br style="clear:both;font:0/0">',this.x=1));

However, this expression is evaluated over and over again. Using runtimeStyle instead avoids this. Sergey Chikuyonok also pointed out that using innerHTML destroys existing HTML elements that may event handlers attached to them. By using document.createElement and appendChild you can insert the new element without removing all the events attached to other descendant elements.

Containing floats in more modern browsers

There are two popular methods to contain floats in modern browsers. Creating a new block formatting context (as is done in IE 6/7 when hasLayout is triggered) or using a variant of the “clearfix” hack.

Creating a NBFC results in an element containing any floated children, and will prevent top- and bottom-margin collapse of non-floated children. When combined with the enhanced IE 6/7 containment method, it results in consistent cross-browser float containment.

The other method, known as “clearfix”, traditionally used a single :after pseudo-element to clear floats in a similar fashion to a structural, clearing HTML line-break. However, to prevent the top-margins of non-floats from collapsing into the margins of their float-containing ancestor, you also need to use the :before pseudo-element. This is the approach taken in Thierry Koblentz’s “clearfix reloaded”. In contemporary browsers, the micro clearfix hack is also suitable.

The method presented in this article should help improve the results of cross-browser float containment, whether you predominantly use “clearfix” or the NBFC method. The specific limitations of both the “clearfix” and various NBFC methods (as outlined in Thierry’s articles) remain.

Problems

Using a CSS expression to change the DOM in IE 6/7 creates problems of its own. Obviously, the DOM in IE 6/7 is now different to the DOM in other browsers. This affects any JavaScript DOM manipulation that may depend on :last-child or appending new children.

This is still an experimental work-in-progress that is primarily research-driven rather than seeking to become a practical snippet of production code. Any feedback, further testing, and further experimentation from others would be much appreciated.

Thanks to these people for contributing improvements: Jonathan Neal, Mathias Bynens, Sergey Chikuyonok, and Thierry Koblentz.

Applying conditional classnames to the html element is a popular way to help target specific versions of IE with CSS fixes. It was first described by Paul Irish and is a feature of the HTML5 Boilerplate. Despite all its benefits, there are still a couple of niggling issues. Here are some hacky variants that side-step those issues.

An article by Paul Irish, Conditional stylesheets vs CSS hacks? Answer: Neither!, first proposed that conditional comments be used on the opening html tag to help target legacy versions of IE with CSS fixes. Since its inclusion in the HTML5 Boilerplate project, contributors have further refined the technique.

However, there are still some niggling issues with the “classic” conditional comments approach, which Mathias Bynens summarized in a recent article on safe CSS hacks.

1. The Compatibility View icon is displayed in IE8 and IE9 if you are not setting the X-UA-Compatible header in a server config.
2. The character encoding declaration might not be fully contained within the first 1024 bytes of the HTML document if you need to include several attributes on each version of the opening html tag (e.g. Facebook xmlns junk).

You can read more about the related discussions in issue #286 and issue #378 at the HTML5 Boilerplate GitHub repository.

The “bubble up” conditional comments method

Although not necessarily recommended, it looks like both of these issues can be avoided with a bit of trickery. You can create an uncommented opening html tag upon which any shared attributes (so no class attribute) can be set. The conditional classes are then assigned in a second html tag that appears after the <meta http-equiv="X-UA-Compatible"> tag in the document. The classes will “bubble up” to the uncommented tag.

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta http-equiv="X-UA-Compatible"
          content="IE=edge,chrome=1">
    <meta charset="utf-8">
    <!--[if lt IE 7]><html class="no-js ie6"><![endif]-->
    <!--[if IE 7]><html class="no-js ie7"><![endif]-->
    <!--[if IE 8]><html class="no-js ie8"><![endif]-->
    <!--[if gt IE 8]><!--><html class="no-js"><!--<![endif]-->

    <title>Document</title>
  </head>
  <body>
  </body>
</html>

Fork the Gist

The result is that IE8 and IE9 won’t ignore the <meta http-equiv="X-UA-Compatible"> tag, the Compatibility View icon will not be displayed, and the amount of repeated code is reduced. Obviously, including a second html tag in the head isn’t pretty or valid HTML.

If you’re using a server-side config to set the X-UA-Compatible header (instead of the meta tag), then you can still benefit from the DRYer nature of using two opening html tags and it isn’t necessary to include the conditional comments in the head of the document. However, you might still want to do so if you risk not containing the character encoding declaration within the first 1024 bytes of the document.

<!DOCTYPE html>
<html lang="en">
<!--[if lt IE 7]><html class="no-js ie6"><![endif]-->
<!--[if IE 7]><html class="no-js ie7"><![endif]-->
<!--[if IE 8]><html class="no-js ie8"><![endif]-->
<!--[if gt IE 8]><!--><html class="no-js"><!--<![endif]-->
  <head>
    <meta charset="utf-8">
    <title>Document</title>
  </head>
  <body>
  </body>
</html>

Fork the Gist

The “preemptive” conditional comments method

Another method to prevent the Compatibility View icon from showing was found by Julien Wajsberg. It relies on including a conditional comment before the DOCTYPE. Doing this seems to help IE recognise the <meta http-equiv="X-UA-Compatible"> tag. This method isn’t as DRY and doesn’t have the character encoding declaration as high up in the document, but it also doesn’t use 2 opening html elements.

<!--[if IE]><![endif]-->
<!DOCTYPE html>
<!--[if lt IE 7]><html class="no-js ie6"><![endif]-->
<!--[if IE 7]><html class="no-js ie7"><![endif]-->
<!--[if IE 8]><html class="no-js ie8"><![endif]-->
<!--[if gt IE 8]><!--><html class="no-js"><!--<![endif]-->
  <head>
    <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
    <meta charset="utf-8">
    <title>Document</title>
  </head>
  <body>
  </body>
</html>

Fork the Gist

While it’s interesting to explore these possibilities, the “classic” method is still generally the most understandable. It doesn’t create invalid HTML, doesn’t risk throwing IE into quirks mode, and you won’t have a problem with the Compatibility View icon if you use a server-side config.

If you find any other approaches, or problems with those posted here, please leave a comment but also consider adding what you’ve found to the relevant issues in the HTML5 Boilerplate GitHub repository.

Thanks to Paul Irish for feedback and suggestions.

CSS is a versatile style language that is most frequently used to control the look and formatting of an HTML document based on information in the document tree. But there are some common publishing effects – such as formatting the first line of a paragraph – that would not be possible if you were only able to style elements based on this information. Fortunately, CSS has pseudo-elements and pseudo-classes.

As their names imply, they are not part of the DOM in the way that ‘real’ HTML elements and classes are. Instead, they are CSS abstractions that provide additional, and otherwise inaccessible, information about the document.

This article will discuss the CSS pseudo-elements that are part of CSS 2.1 – :first-letter, :first-line, :before, and :after – and how the :before and :after pseudo-elements can be exploited to create some interesting effects, without compromising the simplicity of your HTML. But first, let’s look at each type of pseudo-element and how to use them in their basic form.

The :first-line and :first-letter pseudo-elements

The :first-line pseudo-element lets you apply styles to the first formatted line of a block container element (i.e., elements with their display property set to block, inline-block, list-item, table-caption, or table-cell). For example:

p:first-line { font-weight: bold; }

…will change the first line of every paragraph to bold. The :first-line pseudo-element can be treated as if it were an extra HTML inline element wrapping only the first line of text in the paragraph.

The :first-letter pseudo-element lets you apply styles to the first letter (and any preceding punctuation) of the first formatted line of a block container element. No other inline content (e.g. an image) can appear before the text. For example:

p:first-letter { float: left; font-size: 200%; }

…will produce a basic ‘drop cap’ effect. The first letter of every paragraph will be floated left, and twice as large as the other letters in the paragraph. The :first-letter pseudo-element can be treated as if it were an extra HTML inline element wrapping only the first letter of text in the paragraph.

The :first-line and :first-letter pseudo-elements can only be attached to block container elements, but the first formatted line can be contained within any block-level descendant (e.g., elements with their display property set to block or list-item) in the same flow (i.e., not floated or positioned). For example, the following HTML fragment and CSS:

<div><p>An example of the first line of text being within a descendant element</p></div>

div:first-line { font-weight: bold; }

…would still result in a bold first line of text, because the paragraph’s text is the first formatted line of the div.

The :before and :after pseudo-elements

The :before and :after pseudo-elements are used to insert generated content before or after an element’s content. They can be treated as if they were extra HTML inline elements inserted just before and after the content of their associated element.

Generated content is specified using the content property which, in CSS 2.1, can only be used in conjunction with the :before and :after pseudo-elements. Furthermore, you must declare the content property in order to generate the :before and :after pseudo-elements.

The content property can take string, url(), attr(), counter() and counters() values. The url() value is used to insert an image. The attr() function returns as a string the value of the specified attribute for the associated element. The counter() and counters() functions can be used to display the value of any CSS counters.

For example, the following HTML fragment and CSS:

<a href="http://wikipedia.org">Wikipedia</a>

a:after { content: " (" attr(href) ")"; }

…would display the value of the href attribute after a link’s content, resulting in the following anchor text for the example above: Wikipedia (http://wikipedia.org). This can be a helpful way to display the destination of specific links in printed web documents.

Keep in mind that CSS is meant for adding presentation and not content. Therefore, the content property should be used with caution.

It’s also worth noting that the :first-letter and :first-line pseudo-elements apply to the first letter and first line of an element including any generated content inserted using the :before and :after pseudo-elements.

Browser support for pseudo-elements

The :first-letter and :first-line pseudo-elements were introduced in CSS1 and there is wide basic support for them. However, IE 6 and IE 7 have particularly buggy implementations; even modern browsers are not entirely consistent in the way that they handle the :first-line and :first-letter pseudo-elements (example bugs).

The :before and :after pseudo-elements were introduced in the CSS 2.1 specification and are fully implemented in Firefox 3.5+, IE 8+, Safari 3+, Google Chrome, and Opera. Modern versions of Firefox even support CSS transitions and animations applied to pseudo-elements. However, legacy browsers like IE 6 and IE 7 do not support the :before and :after pseudo-elements at all.

For more detailed information on pseudo-element browser support, browser bugs, and workarounds, have a look at Sitepoint’s reference and this article on IE 6/7 issues.

In most cases, the :before and :after pseudo-elements can be used as part of a ‘progressive enhancement’ approach to design and development, because IE 6 and IE 7 will simply ignore them altogether. Alternatively, Modernizr now includes a robust feature test for generated content, providing one way to specify fallbacks or enhancements depending on browser support. The important thing is to remember to check what happens in browsers where support is missing.

Alternative ways to use pseudo-elements

Let’s take a look at how the :before and :after pseudo-elements can be used as the basis for some interesting effects. Most of the time, this involves generating empty :before and :after pseudo-elements by declaring an empty string as the value of the content property. They can then be manipulated as if they were empty inline HTML elements, keeping your HTML clean and giving you full control of certain effects from within CSS style sheets.

Simple visual enhancements, like speech bubbles and folded corners, can even be created without the need for images. This relies on the fact that you can create simple shapes using CSS.

Several types of ‘CSS polygons’ can be created as a result of browsers rendering borders at an angle when they meet. This can be exploited to create triangles. For example, the following HTML fragment and CSS:

<div class="triangle"></div>

.triangle {
  width: 0;
  height: 0;
  border-width: 20px;
  border-style: solid;
  border-color: red transparent transparent;
}

…will create a downward pointing, red triangle. By varying the width, height, border-width, border-style, and border-color values you can produce different shapes and control their orientation and colour. For more information, be sure to read Jon Rogan’s summary of the technique.

The more advanced pseudo-element hacks use the extra background canvas afforded by each :before and :after pseudo-element. This can help you crop background images, control the opacity of background images, and ‘fake’ multiple backgrounds and borders in browsers without support for CSS3 multiple backgrounds (e.g., IE 8). Taken to ludicrous extremes, you can even build a whole CSS icon set. To start with, let’s look at some simple effects that can be created without images or presentational HTML.

Creating CSS speech bubbles

In this example, a quote is styled to look like a speech bubble, using CSS. This is done by creating a triangle using a pseudo-element, and then absolutely positioning it in the desired place. By adding position:relative to the CSS styles for the HTML element, you can absolutely position the :after pseudo-element relative to its associated element.

<div class="quote">[Quoted text]</div>

.quote {
  position: relative;
  width: 300px;
  padding: 15px 25px 20px;
  margin: 20px auto;
  font: italic 26px/1.4 Georgia, serif;
  color: #fff;
  background: #245991;
}

.quote:after {
  content: "";
  position: absolute;
  top: 100%;
  right: 25px;
  border-width: 30px 30px 0 0;
  border-style: solid;
  border-color: #245991 transparent;
}

There’s nothing stopping you from adding some CSS3 to further enhance the effect for capable browsers. This could be adding rounded corners to the box or applying a skew transform to the triangle itself. Fiddle with the code in this example.

Creating CSS ‘ribbons’

Using the same principle, you can create a CSS ribbon effect without images or extra HTML. This time the effect uses 2 pseudo-element triangles. The HTML fragment is still very simple.

<div class="container">
    <h1>Simple CSS ribbon</h1>
    <p>[other content]</p>
</div>

You then need to use negative margins to pull the h1 outwards so that it extends over the padding and beyond the boundaries of the container div. The HTML fragment above can be styled using the following CSS:

.container {
  width: 400px;
  padding: 20px;
  margin: 20px auto;
  background: #fff;
}

.container h1 {
  position: relative;
  padding: 10px 30px;
  margin: 0 -30px 20px;
  font-size: 20px;
  line-height: 24px;
  font-weight: bold;
  color: #fff;
  background: #87A800;
}

From here, you only need to add the pseudo-element triangles to create the ‘wrapping’ appearance associated with ribbons. The :before and :after pseudo-elements share many styles, so you can simplify the code by only overriding the styles that differ between the two. In this case, the triangle created with the :after pseudo-element must appear on the opposite side of the heading, and will be a mirror image of the other triangle. So you need to override the shared styles that control its position and orientation.

.container h1:before,
.container h1:after {
  content: "";
  position: absolute;
  top: 100%;
  left: 0;
  border-width: 0 10px 10px 0;
  border-style: solid;
  border-color: transparent #647D01;
}

/* override shared styles */
.container h1:after {
  left: auto;
  right: 0;
  border-width: 0 0 10px 10px;
}

Fiddle with the code in this example.

Creating CSS folded corners

The final example of this form of pseudo-element hack creates a simple CSS folded-corner effect. A pseudo-element’s border properties are set to produce two differently-coloured touching triangles. One triangle is a slightly darker or lighter shade of the box’s background colour. The other triangle matches the background colour of the box’s parent (e.g. white). The pseudo-element is then positioned in the top right corner of its associated element to complete the effect.

.note {
  position: relative;
  padding: 20px;
  margin: 2em 0;
  color: #fff;
  background: #97C02F;
}

.note:before {
  content: "";
  position: absolute;
  top: 0;
  right: 0;
  border-width: 0 16px 16px 0;
  border-style: solid;
  border-color: #658E15 #fff;
}

Varying the size of the borders will vary the size and angle of the folded-corner. Fiddle with the code in this example.

Pseudo background-crop

Although creating polygons with pseudo-elements can produce some popular effects without images, the possibilities are inherently limited. But this is only one type of :before and :after pseudo-element hack. Treated as extra background canvases, they can be used to fill some gaps in existing browser support for CSS features.

One of those features is the cropping of background images. In the future, it’s likely that you’ll be able to crop background images using fragment identifiers, as is proposed in the CSS Image Values Module Level 3 draft. But at the moment no browsers support the use of fragment identifiers with bitmap images. Until they do, you can make use of this CSS 2.1 hack to emulate background image cropping in modern browsers.

The principle behind a ‘pseudo background-crop‘ is to apply a background-image to a pseudo-element rather than directly to an element in the HTML document. One of the applications of this technique is to crop icons that are part of a sprite.

For example, a web app might allow users to ‘save’, ‘edit’, or ‘delete’ an item. The HTML involved might look something like this:

<ul class="actions">
  <li class="save"><a href="#">Save</a></li>
  <li class="edit"><a href="#">Edit</a></li>
  <li class="delete"><a href="#">Delete</a></li>
</ul>

To enhance the appearance of these ‘action’ links, it is common to see icons sitting alongside the anchor text. For argument’s sake, let’s say that the relevant icons are part of a sprite that is organised using a 16px × 16px grid.

The :before pseudo-element – with dimensions that match the sprite’s grid unit – can be used to crop and display each icon. The sprite is referenced as a background image and the background-position property is used to control the precise positioning of each icon to be shown.

.actions a:before {
  content: "";
  float: left;
  width: 16px;
  height: 16px;
  margin: 0 5px 0 0;
  background: url(sprite.png);
}

.save a:before { background-position: 0 0; }
.edit a:before { background-position: -16px 0; }
.delete a:before { background-position: -32px 0; }

Using pseudo-elements like this helps to avoid the need to either add liberal amounts of white space to sprites or use empty HTML elements to do the cropping. Fiddle with the code in this example.

Pseudo background-position

The CSS 2.1 specification limits the values of background-position to horizontal and vertical offsets from the top-left corner of an element. The CSS Backgrounds and Borders Module Level 3 working draft includes an improvement to the background-position property to allow offsets to be set from any side. However, Opera 11+ is currently the only browser to have implemented it.

But by using pseudo-elements, it’s possible to emulate positioning a background image from any side in any browser with adequate CSS 2.1 support –’pseudo background-position‘.

Once a pseudo-element is created, it must be absolutely positioned in front of the associated element’s background but behind its content, so as not to prevent users from being able to select text or click on links. This is done by setting a positive z-index on the element and a negative z-index on the pseudo-element.

#content {
  position: relative;
  z-index: 1;
}

#content:before {
  content: "";
  position: absolute;
  z-index: -1;
}

Now the pseudo-element can be sized and positioned to sit over any area within (or beyond) the element itself, without affecting its content. This is achieved by using any combination of values for the top, right, bottom, and left positional offsets, as well as the width, and height properties. It is the key to their flexibility.

In this example, a 200px × 300px background image is applied to the pseudo-element, which is also given dimensions that match those of the image. Since the pseudo-element is absolutely positioned, it can be offset from the bottom and right of the associated HTML element.

#content {
  position: relative;
  z-index: 1;
}

#content:before {
  content: "";
  position: absolute;
  z-index: -1;
  bottom: 10px;
  right: 10px;
  width: 200px;
  height: 300px;
  background: url(image.jpg);
}

Many other hacks and effects are possible using the :before and :after pseudo-elements, especially when combined with CSS3. Hopefully this introduction to pseudo-elements, and how they can be exploited, will have inspired you to experiment with them in your work.

The future of pseudo-elements

The way that pseudo-elements are used will continue to change as CSS does. Some new applications will emerge, and existing ones will fade away as browser implementation of ‘CSS3 modules’ continues to improve.

Generated content and pseudo-elements themselves are likely to undergo changes too. The CSS3 Generated and Replaced Content Module introduced a two-colon format for pseudo-elements (i.e., ::before) to help distinguish between pseudo-classes and pseudo-elements. But for compatibility with previous levels of CSS, pseudo-elements do not require two colons. Most modern browsers support both formats, but it is not supported by IE 8 and the single-colon format ensures greater backwards compatibility.

The proposed extensions to pseudo-elements included the addition of nested pseudo-elements (::before::before), multiple pseudo-elements (::after(2)), wrapping pseudo-elements (::outside), and the ability to insert pseudo-elements into later parts of the document (::alternate). However, the CSS3 Generated and Replaced Content Module is undergoing significant changes.

This article was originally published in .net magazine in April 2011

Related resources

• Interactive examples of the code throughout this article
• CSS generated content techniques
• Automatic numbering with CSS counters
• CSS image replacement using pseudo-elements
• Multiple backgrounds and borders with CSS 2.1
• CSS background image hacks
• A whole bunch of amazing stuff pseudo-elements can do

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