What is a pseudo-element selector?

Pseudo-element selectors are a type of selector in CSS that are used to select specific parts of an element or generate additional content. They allow developers to change it through CSS styles without modifying the HTML structure. The appearance and behavior of the element. Pseudo-element selectors start with a double colon to distinguish pseudo-class selectors. In old versions of CSS, pseudo-element selectors use a single colon. According to the latest CSS specifications, pseudo-element selectors should use double colons, and their syntax is: "::pseudo-element {/* CSS properties and values ​​*/}".

The operating system for this tutorial: Windows 10 system, DELL G3 computer.

Pseudo-element selector is a type of selector in CSS that is used to select a specific part of an element or generate additional content. They allow developers to change the appearance and behavior of elements through CSS styles without modifying the HTML structure.

Pseudo element selectors start with a double colon (::) to distinguish pseudo class selectors. In older versions of CSS, pseudo-element selectors used a single colon (:). However, according to the latest CSS specification, pseudo-element selectors should use double colons (::).

The syntax of the pseudo-element selector is as follows:

::pseudo-element {
    /* CSS属性和值 */
}

Common uses of the pseudo-element selector include:

1. ::before: Insert before the content of the selected element generated content.

2. ::after: Inserts the generated content after the content of the selected element.

3. ::first-letter: Select the first letter of the selected element.

4. ::first-line: Select the first line of the selected element.

5. ::selection: Select the text selected by the user.

Here are some examples of using pseudo-element selectors:

1. Insert an icon before the paragraph:

p::before {
    content: url(icon.png);
}
2. 在链接之后插入一个箭头图标：
a::after {
    content: url(arrow.png);
}

3. Set the background color of the selected text:

::selection {
    background-color: yellow;
}

The advantage of the pseudo-element selector is that it can achieve some effects that cannot be achieved in the HTML structure through CSS styles, thus improving the flexibility and efficiency of developers. However, it is important to note that pseudo-element selectors can only select specific parts of an element, not the entire element. Additionally, different browsers may have varying degrees of support for pseudo-element selectors, so compatibility testing is required when using pseudo-element selectors.

In short, the pseudo-element selector is a powerful selector in CSS that can achieve various effects by generating additional content or changing specific parts of the element. It is an important tool for developers to change the appearance and behavior of elements through CSS styles without modifying the HTML structure.

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