伪类 伪元素

伪类  伪元素 

CSS中：和：： - CSDN博客 https://blog.csdn.net/u014527697/article/details/81087139

 Pseudo-elements - CSS: Cascading Style Sheets | MDN https://developer.mozilla.org/en-US/docs/Web/CSS/Pseudo-elements

A CSS pseudo-element is a keyword added to a selector that lets you style a specific part of the selected element(s). For example, ::first-line can be used to change the font of the first line of a paragraph.

/* The first line of every <p> element. */
p::first-line {
  color: blue;
  text-transform: uppercase;
}

Pseudo-elements - CSS: Cascading Style Sheets | MDN https://developer.mozilla.org/en-US/docs/Web/CSS/Pseudo-elements