CSS 中的双冒号 (::) 是什么意思？
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What does the double colon (::) mean in CSS?
提问by Dilhan Jayathilake
What does the double colon (::) mean in CSS?
::CSS中的双冒号 ( ) 是什么意思？
For example:
例如：
input[type=text]::-ms-clear { display: none; }
采纳答案by alex
It means pseudo elementselector. It means the elementto the right doesn't exist in the normal DOM, but can be selected.
这意味着伪元素选择器。这意味着右侧的元素在普通 DOM 中不存在，但可以被选中。
A pseudo-element is made of two colons (::) followed by the name of the pseudo-element.
伪元素由两个冒号 (::) 后跟伪元素的名称组成。
It was originally only a single colon, but was changed to differentiate it from pseudo classes(like :hover, :first-child, :notetc). It's best to use :for beforeand afterpseudo elements since the single colon has better browser support, namely in earlier IE versions.
它最初只有一个冒号，而是改为从区分其伪类（如:hover，:first-child，:not等）。最好使用:forbefore和after伪元素，因为单冒号有更好的浏览器支持，即在早期的 IE 版本中。
回答by Niels Keurentjes
The ::operator indicates you are selecting a pseudo element, one which does not actually exist as an element but can still be targeted for styling.
该::运营商表示你选择一个伪元素，其中一个实际上并不存在的元素，但仍然可以有针对性地进行造型。
Example of this include several vendor-specific implementations such as the -ms-clearsample you provide, most browsers also have pseudo elements to style scroll bars and other native UI elements, but there are also a lot of predefined pseudo elementswhich can be referenced for practical reasons, such as first-lineand first-letter.
这方面的示例包括几个特定于供应商的实现，例如-ms-clear您提供的示例，大多数浏览器还具有用于样式化滚动条和其他本机 UI 元素的伪元素，但也有许多预定义的伪元素可以出于实际原因进行引用，比如first-line和first-letter。
The :beforeand :afterpseudo elements even allow you to insert actual content into the page using CSS with the contentrule.
在:before和:after伪元素甚至允许你插入实际内容为使用CSS与网页content的规则。
回答by Eric Jablow
CSS3 changes the way pseudo-elements are selected, as the W3C wanted to distinguish pseudo-classes like a:visitedfrom pseudo-elements like p::first-line. See Advanced CSS Selectors.
CSS3 改变了选择伪元素的方式，因为 W3C 希望区分a:visited像p::first-line. 请参阅高级 CSS 选择器。
