Talking about the slider specifically, I'm of course not advocating for going out and rewriting all sliders using shaders.
This is just an example of a place where you can use a shader to create a cool, interactive visual effect.
On the example site I've implemented the slider as a regular HTML slider element, and using a canvas to replace its visual appearance. Doing something like this, I don't believe there's anything in the way of getting all the accessibility benefits of a regular slider element, though I could be wrong, I'm no expert by any means.
Maybe you could do some research, since you're introducing a technology that could easily make accessibility worse or impossible.
However, from what I can see, it probably is accessible, as it is still usable without a mouse, which is an easy first test.
(Though, in Safari, neither slider test has any kind of slider, so there are other big problems.)
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