The thing is, HTML5 introduced the 'semantic' elements (<nav>, <video> etc.) which let the browser know what it is that it's supposed to be displaying. That mea

The thing is, HTML5 introduced the 'semantic' elements (<nav>, <video> etc.) which let the browser know what it is that it's supposed to be displaying. That means that an HTML5 page without any CSS or JavaScript could be understood by the browser and displayed exactly like a native application would be on the platform: the same visual style, the same accessibility features, the same behaviour for keyboard shortcuts or touch gestures. With HTML <5 (and excluding XHTML from the discussion) the browser has no clue what all those <div> and <table> elements are supposed to be, so CSS and JS are necessary to reproduce basic things like screenreader flow for all but the most basic page layouts. Ironically, the opportunity for users' browser to apply stylesheets on generic, semantically meaningful sites was one of the original concepts behind CSS (hence 'cascading' in the acronym - the browser takes precedence), which is now usually employed to overwrite the browsers' defaults!