What is the difference between css id and class

Difference: 1. The prefix symbol of the id selector is "#", and the prefix symbol of the class selector is ".". 2. ID can only appear once in the page, and class can be called multiple times in the page. 3. ID determines the structure and content of the page first, and then defines the style for it; while class is the opposite.

The operating environment of this tutorial: Windows 7 system, CSS3&&HTML5 version, Dell G3 computer.

When defining styles, sometimes the usage of id and class are confused, so here is a special explanation:

The id and class attributes are two common attributes in web pages. They work together to make the entire page colorful. When we define a style for an element. You can use id or class.

• When writing in a CSS style sheet, the prefix symbol '#' should be added before the id selector, and the prefix symbol '.' should be added before the class selector.

• The id attribute can generally only be used once in a page, while the class can be referenced multiple times. As a tag of an element, id is used to distinguish different structures and contents, while class is a style that can be applied to any structure and content.

• In terms of layout ideas, we generally adhere to this principle: id determines the structure and content of the page first, and then defines the style for it: on the contrary, class defines a class first. Styles, and then apply class styles to different elements and content on the page as needed.

Currently, browsers allow multiple IDs with the same attribute value to appear on the same page. Under normal circumstances, they can be displayed normally, but when using JavaScript to control elements through IDs An error will occur.

In practical applications, class is more often used in text sections and page modifications, while id is more often used to implement grand layouts and design containing blocks or containing box styles.

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