Why don't :before and :after pseudo elements w

问题:

This question already has an answer here:

• Does :before not work on img elements? 6 answers
• CSS :after not adding content to certain elements 3 answers

I am trying to use a :before pseudo element with an img element.

Consider this HTML and CSS...

HTML

<img src="http://0.gravatar.com/avatar/this-is-not-a-hash" alt="" />

CSS

img:before {
  content: "hello";
}

jsFiddle.

This does not produce the desired effect (tested in Chrome 13 and Firefox 6). However, it works with a div or span element.

Why not?

Is there a way to make pseudo elements work with img elements?

回答1:

The spec says...

Note. This specification does not fully define the interaction of :before and :after with replaced elements (such as IMG in HTML). This will be defined in more detail in a future specification.

I guess this means they don't work with img elements (for now).

Also see this answer.

回答2:

Just for testing and knowing it's not pretty you can do the following to make the pseudo elements work with 'img' elements.

Add: display: block; content: ""; height: (height of image)px to the img element in your CSS.

Though it will render your img tag empty cause of the content: "" you can then

Add: style="background-image: url(image.jpg)" to your img element in html.

Tested this in Fx, Chrome and Safari

回答3:

It could be that browser vendors have not implemented pseudo elements on the img tag because of their interpretation of the spec: the img element, strictly speaking, is not a block level element or an inline element, it is an empty element.