Pseudo-classes apply styles to elements based on their state or position in the document tree.
:Hover
The :hover pseudo-class applies styles when the user hovers over an element.
a:hover {
    color: red;
}:Focus
The :focus pseudo-class applies styles when an element receives focus, such as when a user clicks on an input field.
input:focus {
    border-color: blue;
}:Nth-child(n)
The :nth-child(n) pseudo-class applies styles to the nth child of a parent element
li:nth-child(odd) {
    background-color: lightgrey;
}:First-child
The :first-child pseudo-class applies styles to the first child of a parent element.
p:first-child {
    font-weight: bold;
}CSS Pseudo-classes Example Code
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>CSS Pseudo-classes Example</title>
    <style>
        a:hover {
            color: red;
        }
        input:focus {
            border-color: blue;
        }
        li:nth-child(odd) {
            background-color: lightgrey;
        }
        p:first-child {
            font-weight: bold;
        }
    </style>
</head>
<body>
    <a href="#">Hover over this link</a>
    <br><br>
    <input type="text" placeholder="Focus on me">
    <br><br>
    <ul>
        <li>Item 1</li>
        <li>Item 2</li>
        <li>Item 3</li>
        <li>Item 4</li>
    </ul>
    <p>This is the first paragraph.</p>
    <p>This is another paragraph.</p>
</body>
</html>


