The similarities and differences between :before and ::before

• Same points

1. can be used to represent pseudo-class objects, used to set The content before the object

2. :before and ::before writing are equivalent

• Differences

1. ##:before is the writing method of Css2, ::before is the writing method of Css3

2. :before has better compatibility than ::before, but it is recommended to use ::before in H5 development

Notes:

Pseudo-class objects should be used together with the content attribute

Pseudo-class objects will not appear in the DOM, so they cannot be operated through js. They are only added to the CSS rendering layer

Pseudo-class objects Special effects usually use the :hover pseudo-class style to activate

##.test:hover:: before {

/* This is when animation and transition take effect */ }

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