Fitt's Law
GoPro
On this website, you can see how the fitt's law was used. There is a button on the bottom of the screen, which is really easy to reach with the finger and it is also big enough to see and not to miss it.
PARC: Repetition
Coursera
In this example, you can see how the repetition was used. The font and sizes are the same as you go through it. Also, the images that are used on the web page are in the same style.
PARC: Contrast
Disney
The Disney website is an example of the contrast principle. By the sizes and colors, you can notice the important details that are there. And it helps your eyes to see the web page as a whole picture.