What is a source pseudo element?

Source pseudo-elements are a special type of pseudo-element in CSS. They allow developers to insert content before or after elements in the DOM. Unlike ordinary pseudo-elements, pseudo-elements actually create a New elements, not just changing the styles of existing elements. Source pseudo-elements were first introduced in the CSS2 specification and further extended and improved in CSS3. They are used to insert content at a specific position of an element in the DOM without adding additional markup or elements in the HTML. This makes Developers can more flexibly control the style and layout of pages.

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

Source pseudo-elements (pseudo-elements) are a special type of pseudo-elements in CSS that allow developers to insert content before or after elements in the DOM. Unlike ordinary pseudo-classes, pseudo-elements actually create a new element rather than just changing the style of an existing element.

Source pseudo-elements were first introduced in the CSS2 specification and were further expanded and improved in CSS3. They are used to insert content at a specific position of an element in the DOM without adding additional markup or elements in the HTML. This allows developers to more flexibly control the style and layout of the page.

The syntax for source pseudo-elements uses a double colon (::) as a prefix, followed by the name of the pseudo-element. The following are some commonly used source pseudo-elements:

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

2. ::after: Insert content after the content of the element.

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

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

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

Using source pseudo-elements can achieve some interesting effects and functions. For example, you can use ::before and ::after to add decorative elements such as arrows, icons, or background images. You can use ::first-letter and ::first-line to change the style of text, such as font size, color, or line height. ::selection can be used to change the background color or text color of user-selected text.

The use of source pseudo-elements is similar to selectors. You can select elements by their class name, ID, tag name, or other selectors, and use pseudo-elements to define styles. For example, the following CSS code will insert an arrow before the element with class "box":

.box::before {
  content: "→";
}

It should be noted that the content attribute of the source pseudo-element is required to define the content to be inserted. Content. This can be text, images, counters, or other visual elements. If you do not set the content attribute, the pseudo element will not be displayed.

In short, the source pseudo-element is a powerful tool in CSS that can insert content before or after elements in the DOM. They are distinguished from ordinary pseudo-classes by using a double colon (::) as a prefix, and provide rich selectors and attributes to define styles. Using source pseudo elements, developers can achieve more flexible and creative page layout and style effects.

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