在现代网页设计中，为文章页面添加引人入胜的视觉效果已成为提升用户体验的关键。其中一种流行的设计模式是，当用户向下滚动页面时，文章主体内容从页面中部向上滑动，逐渐覆盖一个固定不动的背景图片，从而营造出一种视差（parallax）或沉浸式阅读的体验。虽然这种效果可以通过javascript监听滚动事件来实现，但纯css方案往往能提供更优的性能和更简洁的代码。
核心概念：CSS固定背景与可滚动容器
实现此效果的核心在于两个关键CSS特性：
- background-attachment: fixed;: 这个属性使得元素的背景图像相对于视口（viewport）固定。这意味着当元素本身或其父容器滚动时，背景图像不会随之滚动，而是保持在屏幕上的固定位置。
- 可滚动容器: 创建一个占据整个视口高度并允许垂直滚动的容器。文章内容将放置在此容器内，并利用其自身的滚动机制来展现。
通过将一个带有fixed背景的容器设置为页面的主滚动区域，并将文章内容初始定位在视口中间，我们便能巧妙地实现内容向上滚动覆盖固定背景的效果。
实现步骤
我们将通过一个具体的文章页面示例来演示如何构建这种布局。
1. HTML 结构
首先，定义页面的基本HTML结构。main元素将作为我们的主滚动容器，其中包含一个用于包裹所有文章内容的div.articles，以及一个或多个div.article-container来展示具体的文章内容。
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滚动覆盖固定背景文章页
文章标题一
2023年10月27日
这是文章的简要描述，引人入胜。
Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum. Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.
文章标题二
2023年10月27日
这是第二篇文章的简要描述。
Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages.
2. CSS 样式
接下来是关键的CSS样式，它将实现我们所需的效果。
body {
margin: 0; /* 移除默认的body外边距 */
overflow: hidden; /* 防止body自身滚动，将滚动行为委托给main元素 */
}
main {
display: flex;
flex-direction: column;
/* 设置背景图片，并使用 fixed 实现固定效果 */
background: url("https://source.unsplash.com/iuyR_HEwk24/1600x900") no-repeat center fixed;
background-size: cover; /* 确保背景图片覆盖整个容器 */
height: 100vh; /* main元素占据整个视口高度 */
overflow-y: overlay; /* 允许main元素垂直滚动。overlay在支持时不会占用滚动条空间 */
/* 注意：对于不支持 overlay 的浏览器，会回退到 scroll */
}
.articles {
display: flex;
flex-direction: column;
align-items: center; /* 水平居中文章容器 */
justify-content: center; /* 垂直居中（如果内容不够长） */
width: 100%;
margin-top: 50vh; /* 初始时将文章内容推到视口中间，使其从下方出现 */
}
.article-container {
display: flex;
flex-direction: column;
align-items: center;
justify-content: center;
margin: 15px;
width: 45vw; /* 控制文章内容宽度 */
padding: 30px;
color: #1a2434;
background-color: white;
box-shadow: rgba(0, 0, 0, 0.35) 0px 5px 15px;
border-radius: 15px;
/* 确保内容足够长，以便触发滚动效果 */
line-height: 1.6;
}
.article-container h1 {
font-size: 2.5rem;
margin-bottom: 10px;
text-align: center;
}
.article-container .date {
font-size: 0.9rem;
color: rgba(0, 0, 0, 0.6);
margin-bottom: 20px;
}
.article-container .article-description {
font-size: 1.1rem;
font-weight: bold;
margin-bottom: 20px;
text-align: center;
}
.article-container p {
font-size: 1rem;
text-align: justify;
}
/* 为最后一个文章容器增加底部外边距，确保滚动到底部时有足够的空间 */
.article-container:last-child {
margin-bottom: 30px;
}
