Compatibility issues between html and web xhtml_html/css_WEB-ITnose

When I make a web page, there are two parts, one is the product navigation bar, and the other is the automatic switching advertisement. When I use an html file to run it, it works normally (the product navigation bar is on the left, and the automatic switching advertisement is on the right. right next to each other), but when running it in an aspx file using WEB, the two parts are overlapped. What should I do? Thanks!

Reply to the discussion (solution)

Maybe the CSS is incompatible, let’s debug it,
Just rely on these few sentences It is impossible for others to know the problem