Change background from bottom to top on hover

问题

How I can change the background-color on a:hover using a transition from the bottom to the top with a duration of 0.3s?

<ul>
  <li><a></a></li>
  <li><a></a></li>
  <li><a></a></li>
</ul>

Is that possible?

Thanks

回答1:

There is no way to (generically) apply a transition direction in CSS. However, we can work around that limitation by using a pseudo element (or other method like how this example uses gradients).

By using a pseudo element, which initially has a visible height of 0, we can transition the height from and to a desired direction when the link is hovered. It's best to use transform: scale for performance reasons, which means that we need to set our transform-origin to bottom center in this case to make sure it goes from bottom to top.

This approach is probably the most general, working with non-solid backgrounds and such, but does require a pseudo element or child element.

The CSS for that approach would be:

li {
    background: red;
}
a {
    position: relative;
    z-index: 1;
}
a::after {
    content: "";
    position: absolute;
    bottom: 0;
    left: 0;
    width: 100%;
    height: 100%;
    transform: scaleY(0);
    transform-origin: bottom center;
    background: blue;
    z-index: -1;
    transition: transform 0.3s;
}
a:hover::after {
    transform: scaleY(1);
}

Demo

来源：https://stackoverflow.com/questions/20659605/change-background-from-bottom-to-top-on-hover