No. In the strict sense, you cannot. HTML was mainly designed to develop and share documents written for the browser (and CSS provides layout information for such a document).
Although, this is no longer the case. There are many possibilities when HTML and CSS are used outside of the browser (for example, Gnome Shell is developed using CSS and Javascript or thinks of a Modern User Interface for Windows 8).
So, if you are considering Windows 8, it is possible to create an application outside the browser; but technically this is not. .exeThis is not an executable file.
Another possibility is to use the WebBrowser Class , which allows you to write .exe, which uses your HTML and CSS.
So, there are ways to embed HTML in an executable file, but you cannot make it executable on your own, as it is a document / markup language, not a programming language and cannot be converted to working code.