Panels not displaying correctly in Visual studio

I am designing an ASP.NET web page using Visual Studio. The web page has one large panel at the top of the page and two smaller panels side by side below it. The two lower panels sit side by side by using the CSS float property.

When I view the web page in my web browser it is displayed correctly. But when I view the page in Design view in Visual Studio, the two lower panels appear one above the other, instead of side by side. It appears this is a problem with Visual Studio itself as when I close the Properties window at the right hand side to make more space for the editor, the panel pops up next to the other one where it should be.

I was wondering if there is a setting in Visual Studio I can change to stop this happening so I can view the page in the Design editor as it should be? Or is there no setting to do that and maybe it is to do with my code? Hope this makes sense!