悬停时从底部到顶部更改背景 [英] Change background from bottom to top on hover

问题描述

如何在 a：hover 上改变背景颜色，使用从底部到顶部的过渡时间为0.3秒？

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>

有可能吗？

/ p>

Thanks

推荐答案

没有办法（一般地）在CSS中应用转换方向。但是，我们可以通过使用伪元素（或其他方法，例如

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).

通过使用初始具有可见高度为0的伪元素，当链接被悬停时将高度从期望方向过渡到期望方向。由于性能原因，最好使用 transform：scale ，这意味着我们需要将 transform-origin 设置为底部中心在这种情况下，以确保它从底部到顶部。

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.

这种方法可能是最常见的，使用非实体背景等，但确实需要一个伪元素。

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

这种方法的CSS将是：

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);
}

演示

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