You need to serve it with the right mime time (application/xhtml+xml) or in case of local files use .xhtml extension. Then it's processed as XHTML and rendered

You need to serve it with the right mime time (application/xhtml+xml) or in case of local files use .xhtml extension. Then it's processed as XHTML and rendered as expected. Also you need namespace declaration otherwise it will be rendered as unstyled xml. This is all part of HTML5 spec: https://html.spec.whatwg.org/#the-xhtml-syntax https://html.spec.whatwg.org/#the-xhtml-syntax