Nice and simple, very responsive!

I did something similar a long time back, but not really focused on something that tiles up: https://svg-generator.netlify.app/

This is not tilling as the edges does not match the opposite side.

Seems to have some issues on mobile devices.

It looks just like a hotel carpet.

I think what would be useful for such a site is a README or HOWTO that shows step-by-step how to make an app like this. It does not have to be complete, or even nearly complete, the description for the unique parts would suffice. For example, for this site SVG format does not have to be described a reference or two would do. That being said, this is a neat idea. I like it! I'd like it more if I had pointers on how to modify or extend it.