Pseudo-classes allow adding CSS rules to certain parts of the same selector.
For example, when you define a style for a HTML tag or a particular class, the content of all those tags or class will have the same style. If you want to define a different style for the first (or last) element of those tags or for the first content of a group of elements with the same class, you can accomplish this by using pseudo-classes.
Also, they can change the graphic style of items when the mouse is acting on them.
To understand CSS pseudo-classes, how they work and what is their effect, study the following examples.
Type selectors refer to HTML tags which they define (eg.: p for <p>, li for <li>, div for <div>, etc.).
In the following example is used first-child with paragraphs.
<style>
p:first-child {
color:blue;
}
</style>
<h4>Example first-child</h4>
<blockquote>Apply css style to first P tag.</blockquote>
<div>
<p>A text within the first paragraph</p>
<p>Content in the second paragraph</p>
<p>Text content in the third paragraph</p>
</div>
hover value applied to <li> tags.
<style>
li:hover {
background-color:#88fe88;
}
</style>
<h4>Example hover</h4>
<p>When you place the mouse over each LI, it will have a green background.</p>
<ul>
<li>Free courses and tutorials</li>
<li>Web site: https://coursesweb.net</li>
<li>Web site: marplo.net</li>
</ul>
class attribute, in stylesheets are added after a (.) character.lang and last-child applied to a class '.test':
<style>
.test:last-child {
background-color:#88fe88;
}
.test:lang(en) {
color:blue;
}
</style>
<h4>Example lang and last-child</h4>
<p>The CSS style defined for <b>test: last-child</b> will be applied to the last LI that has class 'test'.<br>
The CSS rule added to <b>.test:lang(en)</b> is applied only to the element that has both: <em>class='test'</em> and <em>lang='en'</em> attributes.</p>
<ul>
<li class='test'>HTML: https://coursesweb.net/html</li>
<li class='test' lang='en'>CSS: https://coursesweb.net/css</li>
<li class='test'>JavaScript: https://coursesweb.net/javascript</li>
</ul>
<style>
/* Applies to the first EM tag of every element with class='test' */
.test em:first-child {
font-weight: bold;
color: blue;
}
</style>
<p>A CSS style will be applied to first EM tag of every 'test' class.</p>
<p class='test'>Paragraph with three EM tags: <em>blue text</em>, a <em>second EM tag</em>, and another <em>em text</em>.</p>
<p class='test'>Another paragraph: <em>a bold-italic blue string</em>, and a second <em>em sub-string</em>.</p>
hover pseudo-class applied to an ID, and the focus pseudo-class to a class (test).
<style>
#idb:hover {
background-color:#12da34;
}
.test:focus {
background-color:#dadafe;
}
</style>
<h4>Example hover and focus</h4>
<p>When the mouse is over the button it changes its background color.<br>
When you click on the text areas of the form it changes their background color.</p>
<form action='' method='post'>
<input type='text' class='test' /><br />
<textarea cols='20' rows='5' class='test'></textarea><br />
<input type='button' value='Button' id='idb' />
</form>
<table><tr> <th>Title 1</th> <th>Title 2</th> </tr></table>
.some_class {
line-height: 150%;
}document.getElementById("id_button").onclick = function(){
window.open("http://coursesweb.net/");
}$ar_dir = scandir("dir_name");
var_export($ar_dir);