User preference and configurability of hyperTEXT display has been totally thrown under the bus, increasingly throughout the web's existence. I remember when it was straightforward to have your own text color and font preference, and web sites didn't try to override them. You could even configure a brick wall GIF background for sites if you wanted to. Now, these preferences are buried and easy for a developer to ignore using CSS and JavaScript. And as you say, it'll get even worse. The user agent (who, by the way, you're writing your web site for) now has very little say in how a web page is rendered.

Unpopular opinion on HN full of web devs, but I don't want my browser to be a "canvas" for some developer. I don't want it to be a "stable ABI" for some opaque binary app. I already have a platform for binary applications: It's called a desktop operating system. I wish more developers would go back to developing for that and leave the web alone. I want my web browser to display hyperTEXT documents, with links out to other hyperTEXT documents, and occasionally accept input from me via a FORM. And that's it. I understand that opinion makes me a minority nowadays, though. Maybe we should revitalize gopher or something--something to get back to the roots of fetching, displaying, and navigating information.