如何将CSS样式表应用于RSS源

<rss version="2.0">
 <channel>
   <title>RSS源示例</title>
    <link>http://example.com/rss</link>
   <description>这是一个示例RSS源</description>
    <item>
     <title>文章标题1</title>
     <description>文章描述1</description>
      <link>http://example.com/post/1</link>
      <pubDate>Sun, 01 Jan 2023 12:00:00 +0000</pubDate>
     <author>作者名1</author>
     <style>
        body {
          background-color: lightblue;
        }
      </style>
    </item>
  </channel>
</rss>

<rss version="2.0">
 <channel>
   <title>RSS源示例</title>
    <link>http://example.com/rss</link>
   <description>这是一个示例RSS源</description>
    <!-- 使用内部样式覆盖所有RSS项 -->
    <item>
     <title>文章标题1</title>
     <description>文章描述1</description>
      <link>http://example.com/post/1</link>
      <pubDate>Sun, 01 Jan 2023 12:00:00 +0000</pubDate>
     <author>作者名1</author>
    </item>

    <!-- 使用外部CSS文件覆盖特定RSS项 -->
    <item>
     <title>文章标题2</title>
     <description>文章描述2</description>
      <link>http://example.com/post/2</link>
      <pubDate>Mon, 02 Jan 2023 12:00:00 +0000</pubDate>
     <author>作者名2</author>
     <external-link rel="stylesheet" href="http://example.com/rss/styles.css"></external-link>
    </item>
  </channel>
</rss>