When you visit this website, if you look to the right of your screen, you’ll see a couple of icons in a vertically oriented grey rectangle. The top icon is a black circle that is half open, half solid. The lower icon has two black letter Ts in capital case, but of different sizes.
You’ll also notice that these icons stay in place whether you move the image by scrolling up and down or by using your arrow keys.
The top button allows you to shift to a high contrast screen: