CSS selector types and simple applications

These selectors can be grouped into the following categories:

(1) Defines a style for a particular element name so that all of the elements in the Web page can apply the style.

(2) defines a style for a particular class attribute name so that all of the class attribute values in the Web page can be applied to an element of that property name

(3) Defines a style for a particular element that is marked with an id attribute and is also defined using the id attribute value.

(4) For certain purposes defined by the use of the above 3 classes can not implement the selector, including pseudo class and pseudo element selector, etc.

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