Bookmarked! I love the interactive diagrams! I love that you have a touch-point larger than the drag handle. And I'm impressed that the label placement takes care to avoid the axes. Some feedback:

You have vector s in blue, and then vector u in teal, and then vector v in orange.

In the diagram, it's "Subject", "First Reflector", "Second Reflector". I think it'd be better if these labels were "Subject s", "First Reflector u", "Second Reflector v" so that we can match up the text to the diagram even without color.

Later you have "The pair of vector u and v is called a rotor". But these colors do not match the earlier colors, and it makes it hard to connect to the diagram.

In the 3D diagram, I think it would be better if you used the same color scheme as for the 2D diagram. Same for the circular reflection diagram.

Suggested colors:

- subject s - orange in every diagram (currently blue, blue, blue)

- first reflector - teal in every diagram (currently teal, magenta, pink)

- second reflector - blue in every diagram (currently orange, teal, orange)

This makes the rotor colors more similar to each other than to the subject.