Some people like drawing doodles. Others like coloring books.
The point of these type of activities is to relax the mind. I think it is enjoyable to play around with shapes and colors without trying to control the end result.
CSS-only doodle pages
Here are three very basic pages where we can mindlessly play with colors. There is no JS on these pages. As I was playing around with CSS I realised a lot can be done with just HTML tags and CSS animation.
Try it out! Note that these can be (very) slow on mobile devices.
The movement of the pointer has an effect on the tile beneath. The doodle will not end up exactly as we want. We have no real control of the end result. If we move too wildly we might erase the doodle. And, that is okay. The doodle will not be saved.
On devices that support mouse movement the interaction is based on the location of the mouse. On touch devices it is based on tapping on a location. As a result, they play differently based on what device you are using. Personally I prefer the desktop experience.