如果在没有样式表的情况下测试情况，您将看到section元素中的h1以较小的字体显示。 这是由浏览器样式表引起的，在支持section浏览器及其在HTML5中的建议呈现中。 section元素已定义为在其中， h1元素是该节的标题，因此相对于页面整体而言，它位于第二级（或者甚至在较低级别，如果section元素已嵌套）。 
 
 关于这种方法的充分性有各种各样的意见，但这就是HTML5草案所说的以及一些浏览器已经实现的内容。 另一方面，旧浏览器忽略了这些规则，因此该方法实际上并不健壮。 使用h2作为章节标题更安全（并且根据HTML5是完全可以接受的）。 

If you test the situation without your style sheet, you will see that h1 inside a section element appears in a smaller font. This is caused by a browser style sheet, in browsers that support section and its suggested rendering in HTML5. The section element has been defined so that within it, an h1 element is a heading for the section, so relative to the page as a whole, it is at the 2nd level (or even at a lower level, if section elements have been nested).
 
There are various opinions on the adequacy of that approach, but that’s what HTML5 drafts say and what some browsers have implemented. On the other hand, old browsers ignore such rules, so the approach is not practically robust. It is safer (and quite acceptable according to HTML5) to use h2 for section headings.