如何从左到右为下划线设置动画？

Question

我正在尝试从 uber.design 网站复制这种转变：

问题是我被困在扭转过渡：

.un {
  display: inline-block;
}

.un:after {
  content: '';
  width: 0px;
  height: 2px;
  display: block;
  background: black;
  transition: 300ms;
}

.un:hover:after {
  width: 100%;

<span class="un">Underlined Text</span>

Answer 1

您可以使用渐变和延迟调整background-position以获得这样的效果：

.un {
  display: inline-block;
  padding-bottom:2px;
  background-image: linear-gradient(#000, #000);
  background-position: 0 100%; /*OR bottom left*/
  background-size: 0% 2px;
  background-repeat: no-repeat;
  transition:
    background-size 0.3s,
    background-position 0s 0.3s; /*change after the size immediately*/
}

.un:hover {
  background-position: 100% 100%; /*OR bottom right*/
  background-size: 100% 2px;
}

<span class="un">Underlined Text</span>

如果您想要悬停时的连续动画，您可以试试这个：

.un {
  display: inline-block;
  padding-bottom:2px;
  background-image: linear-gradient(#000, #000);
  background-position: right -100% bottom 0;
  background-size: 200% 2px;
  background-repeat: no-repeat;
}

.un:hover {
  background-position: left -100% bottom 0;
  transition: background-position 0.5s;
}

<span class="un">Underlined Text</span>

您可以查看此答案以获取有关如何完成不同值的计算的更多详细信息：Using percentage values with background-position on a linear-gradient

---

另一种动画

.un {
  display: inline-block;
  padding-bottom:2px;
  background-image: linear-gradient(to right, #000 33%,transparent 33% 66%,#000 66%);
  background-position: right bottom;
  background-size: 300% 2px;
  background-repeat: no-repeat;
}

.un:hover {
  background-position: left bottom;
  transition: background-position 0.5s;
}

<span class="un">Underlined Text</span>

让我们不要忘记基本的：

.un {
  display: inline-block;
  padding-bottom:2px;
  background-image: linear-gradient(#000,#000);
  background-position: right bottom; /* OR left bottom*/
  background-size: 100% 2px;
  background-repeat: no-repeat;
  transition: background-size 0.5s;
}

.un:hover {
  background-size: 0% 2px;
}

<span class="un">Underlined Text</span>

您可以在这里找到更多技术：https://dev.to/afif/100-underline-overlay-animation-the-ultimate-css-collection-4p40

Answer 2

您需要将伪元素进行绝对定位并使用:not 选择器来重现此效果。

.un {
  display: inline-block;
  position: relative;
}

.un:after {
  content: '';
  width: 0px;
  height: 2px;
  position: absolute;
  top: 100%;
  left: 0;
  background: black;
  transition: 300ms;
}

.un:hover:after {
  width: 100%;
}

.un:not(:hover):after {
  right: 0;
  left: auto;
}

<span class="un">Underlined Text</span>

Answer 3

没有 :not 选择器或渐变，最简单的解决方案是在左右位置之间切换，例如在代码中。

span.un {
  position: relative;
}

span.un::after {
  position: absolute;
  content: "";
  background: black;
  bottom: 0;
  right: 0;
  height: 2px;
  width: 0%;
  transition: 300ms ease-in-out;
}

span.un:hover::after {
  width: 100%;
  left: 0;
}

<span class="un">Underline me</span>