Hello,
Thank you for providing a working link.
It looks like visual artefacts from the graphic rendering engine of your computer. Can you tell us what kind of:
- Device you use (brand, model...)
- Graphic chipset or card present in it (and its driver version)
- Operating system (and it's version)
To be honest, I'm not sure we'll be able to do anything about it. It seems clearly out of scope regarding CryptPad itself, but I'm sure that could be interesting to others as well.