HTML+CSS：展开动画

要实现一个简单的HTML和CSS展开动画，你可以使用CSS的transition属性和一些JavaScript代码。以下是一个例子：

HTML:




<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Expand Animation</title>
<style>
  .container {
    overflow: hidden;
    max-height: 0;
    transition: max-height 0.3s ease-out;
    background-color: #f5f5f5;
    padding: 10px;
    margin-top: 10px;
  }
  .read-more .btn {
    padding: 10px 20px;
    background-color: #4CAF50;
    color: white;
    border: none;
    text-align: center;
    display: inline-block;
    font-size: 16px;
    cursor: pointer;
  }
  .read-more .content {
    display: none;
  }
</style>
</head>
<body>
 
<div class="read-more">
  <button class="btn">Read More</button>
  <div class="content">
    <p>This is the content that will be revealed when you click the button. It can be any text or HTML content you want to show.</p>
  </div>
</div>
 
<script>
document.querySelector('.read-more .btn').addEventListener('click', function() {
  var content = document.querySelector('.read-more .content');
  content.style.display = 'block';
  setTimeout(function() {
    content.classList.add('container');
  }, 0);
});
</script>
 
</body>
</html>

CSS:




.container {
  overflow: hidden;
  max-height: 0;
  transition: max-height 0.3s ease-out;
  background-color: #f5f5f5;
  padding: 10px;
  margin-top: 10px;
}
 
.read-more .btn {
  padding: 10px 20px;
  background-color: #4CAF50;
  color: white;
  border: none;
  text-align: center;
  display: inline-block;
  font-size: 16px;
  cursor: pointer;
}
 
.read-more .content {
  display: none;
}

JavaScript:




document.querySelector('.read-more .btn').addEventListener('click', function() {
  var content = document.querySelector('.read-more .content');
  content.style.display = 'block';
  setTimeout(function() {
    content.classList.add('container');
  }, 0);
});

这段代码实现了一个按钮点击后内容逐渐展开的效果。通过CSS定义了.container类的初始最大高度为0，并设置了过渡效果。当JavaScript代码监听到按钮点击事件时，它会将内容的display属性设置为'block'，并在下一个事件循环中添加.container类，从而触发最大高度从0到实际内容高度的过渡动画。

HTML+CSS：展开动画

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