What are the forms of css selectors?

The forms of css selectors are: 1. Element selector; 2. Class selector; 3. ID selector; 4. Attribute selector; 5. Pseudo-class and pseudo-element selectors; 6. Combination Selector; 7. Use attribute selector in combination with pseudo-class/pseudo-element. Detailed introduction: 1. Element selector is the most basic selector, which selects elements according to the type of HTML elements; 2. Class selector, which selects elements through the class attributes of HTML elements; 3. ID selector, The element is selected through the ID attribute of the HTML element; 4. Attribute selector, etc.

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

CSS selectors come in many forms, each with different syntax and application scenarios. The following are some common CSS selector forms:

1. Element selector: The element selector is the most basic selector, which selects elements based on the type of HTML element. For example, the p selector will select all paragraph elements.

2. Class selector: The class selector selects elements through the class attributes of HTML elements. Class selectors are represented using the . symbol followed by the class name. For example, the .my-class selector will select all elements with the class name my-class.

3. ID selector: The ID selector selects elements through the ID attribute of HTML elements. ID selectors are represented by the # symbol, followed by the ID name. The ID is unique within the HTML document, so you can use it to style specific elements. For example, the #my-id selector will select the element with the ID my-id.

4. Attribute selector: Attribute selector is used to select elements with specific attributes. Here are some examples of commonly used attribute selectors:

• [attribute]: Selects all elements with the specified attribute.
• [attribute=value]: Selects all elements with the specified attribute and value.
• [attribute~=value]: Selects all elements with the specified attribute value (separated by spaces). For example, the a[href] selector will select all link elements with the href attribute, and the a[href="example.com"] selector will select all link elements with the href attribute value "example.com".

5. Pseudo-class and pseudo-element selectors: Pseudo-class and pseudo-element selectors are used to select elements or specific parts of elements in a specific state. Here are some examples of commonly used pseudo-classes and pseudo-element selectors:

• :hover: Selects the element on mouse hover.
• :active: Select elements activated by the user.
• :visited: Select link elements that have been visited by the user.
• ::before and ::after: Content inserted before or after the element content. For example, the :hover a selector will select all link elements on mouseover, and a::before { content: "text"; } will insert some text before the content of all link elements.

6. Combination selector: Combination selector allows you to select elements based on their relationship with other elements. The following are some examples of commonly used combination selectors:

• Child combinators: Two elements separated by spaces, indicating that the first element is a direct child of the second element. element. For example, the p a selector will select all link elements contained directly within a paragraph.
• Descendant combinators: Two elements separated by a space, indicating that the first element can be any descendant element of the second element. For example, the p a selector will select all link elements contained within a paragraph, no matter how deeply descended they are.
• Adjacent sibling combinators: Two elements separated by a symbol, indicating that the first element is the next sibling element of the second element, and they have the same parent element. For example, the p a selector will select all link elements immediately following a paragraph.
• General sibling combinators: Two elements separated by a space, indicating that the first element can be any sibling element of the second element. For example, the p ~ a selector will select all link elements that follow a paragraph, regardless of how many other sibling elements precede them.

7. Use attribute selectors in combination with pseudo-classes/pseudo-elements: You can also use attribute selectors in conjunction with pseudo-classes/pseudo-elements to create more complex rules. . For example, you can use :hover a[href] to select link elements that have the href attribute on mouseover.

The above are some common selector forms of CSS, but in fact CSS also provides more advanced and complex selector syntax, which can be flexibly applied according to specific needs.

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