What are pseudo-classes and pseudo-elements in web

Pseudo classes and pseudo elements in the web are a special form of CSS selectors used to select and style specific elements. Detailed description: 1. Pseudo-class is a selector used to select a specific state or behavior of an element. It starts with a colon (:) and is used to add additional styles to the element; 2. Pseudo-element is used in front of or in front of the content of the element. Selectors inserted after the generated content, starting with a double colon (::), are used to create some extra content that is not in the HTML structure.

# Operating system for this tutorial: Windows 10 system, Dell G3 computer.

In web development, pseudo-classes and pseudo-elements are special forms of CSS selectors used to select and style specific elements.

1. Pseudo-class: Pseudo-class is a selector used to select a specific state or behavior of an element. They start with a colon (:) and are used to add extra styling to an element. Common pseudo-classes include `:hover` (when the mouse is hovering), `:active` (when the mouse is clicked), `:focus` (when the focus is obtained), etc. For example, you can use the `:hover` pseudo-class selector to style the state when the mouse is hovering over a link:

a:hover {
  color: red;
}

2. Pseudo-element (pseudo-element): Pseudo-element is used in the element Selector to insert generated content before or after the content. They start with a double colon (::) and are used to create some extra content that is not part of the HTML structure. Common pseudo-elements include `::before` (insert content before element content), `::after` (insert content after element content), etc. For example, you can use the `::before` pseudo-element selector to insert a generated content before the element:

p::before {
  content: "前缀：";
  font-weight: bold;
}

Pseudo-classes and pseudo-elements can be used in conjunction with other selectors to select and style specific element. They provide more flexibility and control in styling elements for different states and positions.

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