问题
<!DOCTYPE html>
<html>
<head>
<style>
div
{
transition:after 3s;
-webkit-transition:after 3s;
}
div:hover:after
{
content:"- positive!";
}
</style>
</head>
<body>
<div>Test</div>
</body>
</html>
I have this sample code above. I'm trying to use 'transition' so that the text: '- positive!' takes 3 seconds to slide/show up. But it isn't working.. How to fix it?
回答1:
after is not a valid value of transition.
Instead put transition as a property of the :after selector.
HTML
<div>Test</div>
CSS
div:after {
content:" - positive!";
position: relative;
opacity: 0;
top: -20px;
-webkit-transition: all 3s;
transition: all 3s;
}
div:hover:after {
opacity: 1;
top: 0px;
}
Demo
You can also have a different transition on the hover in and hover out state. This allows us to have a delay to show the pseudo-element but no delay to hide it.
CSS
div:after {
content:" - positive!";
position: relative;
opacity: 0;
top: -20px;
-webkit-transition: all 250ms;
transition: all 250ms;
}
div:hover:after {
opacity: 1;
top: 0px;
-webkit-transition: all 3s;
transition: all 3s;
}
Demo
Here is a list of browsers that support transitions on pseudo elements: http://css-tricks.com/transitions-and-animations-on-css-generated-content/
来源：https://stackoverflow.com/questions/19579340/css-transition-after-a-pseudo-element-how-to-transition-content-that-shows-o