<p>我正在尝试使用 CSS 过渡使 <code></code></p><ul> 向下滑动。<p><br /></p> <p><code></code></p><ul> 从 <code>height: 0;</code> 开始。悬停时，高度设置为 <code>height:auto;</code>。然而，这导致它只是出现，<em>而不</em>过渡，<p><br /></p> <p>如果我从 <code>height: 40px;</code> 到 <code>height: auto;</code>，那么它会向上滑动到 <code>height: 0;</code>，然后突然跳到正确的高度。</p> <p>如果不使用 JavaScript，我还能如何做到这一点？</p> <p><br /></p> <pre class="brush:css;toolbar:false;">#child0 { height: 0; overflow: hidden; background-color: #dedede; -moz-transition: height 1s ease; -webkit-transition: height 1s ease; -o-transition: height 1s ease; transition: height 1s ease; } #parent0:hover #child0 { height: auto; } #child40 { height: 40px; overflow: hidden; background-color: #dedede; -moz-transition: height 1s ease; -webkit-transition: height 1s ease; -o-transition: height 1s ease; transition: height 1s ease; } #parent40:hover #child40 { height: auto; } h1 { font-weight: bold; }</pre> <pre class="brush:html;toolbar:false;">The only difference between the two snippets of CSS is one has height: 0, the other height: 40. &lt;hr&gt; &lt;div id="parent0"&gt; &lt;h1&gt;Hover me (height: 0)&lt;/h1&gt; &lt;div id="child0"&gt;Some content &lt;br&gt;Some content &lt;br&gt;Some content &lt;br&gt;Some content &lt;br&gt;Some content &lt;br&gt;Some content &lt;br&gt; &lt;/div&gt; &lt;/div&gt; &lt;hr&gt; &lt;div id="parent40"&gt; &lt;h1&gt;Hover me (height: 40)&lt;/h1&gt; &lt;div id="child40"&gt;Some content &lt;br&gt;Some content &lt;br&gt;Some content &lt;br&gt;Some content &lt;br&gt;Some content &lt;br&gt;Some content &lt;br&gt; &lt;/div&gt; &lt;/div&gt;</pre> <p><br /></p></ul></ul>

ul {
  background-color: #eee;
  transform: scaleY(0);    
  transform-origin: top;
  transition: transform 0.26s ease;
}
p:hover ~ ul {
  transform: scaleY(1);
}

<p>Hover This</p>
<ul>
  <li>Coffee</li>
  <li>Tea</li>
  <li>Milk</li>
</ul>

ul {
  clip: rect(auto, auto, 0, auto);
  position: absolute;
  margin: -1rem 0;
  padding: .5rem;

  color: white;

  background-color: rgba(0, 0, 0, 0.8);

  transition-property: clip;
  transition-duration: 0.5s;
  transition-timing-function: cubic-bezier(0.175, 0.885, 0.32, 1.275);
}
h3:hover ~ ul,
h3:active ~ ul,
ul:hover {
  clip: rect(auto, auto, 10rem, auto);
}

<h3>Hover here</h3>
<ul>
  <li>This list</li>
  <li>is clipped.</li>
  <li>A clip transition</li>
  <li>will show it</li>
</ul>
<p>
  Some text...
</p>

#menu #list {
    max-height: 0;
    transition: max-height 0.15s ease-out;
    overflow: hidden;
    background: #d5d5d5;
}

#menu:hover #list {
    max-height: 500px;
    transition: max-height 0.25s ease-in;
}

<div id="menu">
    <a>hover me</a>
    <ul id="list">
        <!-- Create a bunch, or not a bunch, of li's to see the timing. -->
        <li>item</li>
        <li>item</li>
        <li>item</li>
        <li>item</li>
        <li>item</li>
    </ul>
</div>