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Learn CSS, part 7: Pseudo Elements

We have discussed CSS selectors in the last three articles in this sereis. We have said that a selector can be a markup element, an attribute selector based on the class and ID attributes, or a structured selector based on the document structure. CSS introduces pseudo elements, which we will be discussing in this article. This is one area of functionality that you can't achieve using HTML, and you will be amazed how easily you can achieve it in CSS.

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By: Michael Youssef

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June 27, 2005

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These pseudo elements give you the ability to insert text or images before (using ::before) the content of the element and after the content of the element (using ::after), through the use of the content property. They are very useful if you have some string values that are repeated in the HTML code a lot. Instead of sending them many times, increasing the size of the page and using more bandwidth, you can send these string values only once in the CSS file (because browsers will cache the CSS file). Use this in Web pages as much as you can, because doing so will save the page size -- but be careful to use generated content, because it has not yet been implemented by IE.

Let's look at an example. In the next CSS code we set the before and after content for any <p> element that has the class QandA (note the power of the combination of element selector, class selector and the pseudo element offered by CSS):

p.QandA
{
background-color: cyan;
color: red;
font-family: Arial;
}
p.QandA::before
{
content: "Question: ";
font-family: Arial;
font-size: 1.1em;
color: white;
background-color: blue;
}
p.QandA::after
{
content: " ?";
font-family: Arial;
font-size: 1.1em;
color: white;
background-color: blue;
}

And here's the HTML code:

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
    <link rel="stylesheet" href="PElements.css" type="text/css">
    <title>CSS Pseudo Elements</title>
</head>
<body>
    <p class="QandA">Do you like CSS</p>
</body>
</html>

The ::before pseudo element has inserted the value of its content property BEFORE the content of the <p> element, and has applied the styling rules too. The same thing applies to the ::after pseudo element.

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