Despite WebGL having been around since 2011, you probably do not run into many websites with 3D. And when you do, its likely a fullscreen game or demo, not a typical website. Traditional web technologies do not mix well with WebGL. Libraries like Voodoo.js try to bridge this gap by allowing you to insert 3D objects inside a normal webpage. Voodoo.js graphics are not anti-aliased when rendering with WebGL, the contrast with the rest of the smooth text and graphics on a webpage then becomes very harsh and downright ugly.
Threepy is an experimental library built on THREE.js that allows some HTML and CSS to be mixed together with WebGL rendering and post-processing FX. The library wraps many standard HTML element types with special hacks like: callbacks, catching events, and rendering to proxy clones. Not every combination of HTML and CSS is compatible with this method. The video below tests the basic UI elements: checkboxes, text input, select drop down lists, number input, color selector, tab menus, slider controls, images and videos. Works with GoogleChrome and NodeWebkit.