When I play online, the text is certain areas is much larger than shown in the screenshots in the documentation.
My zoom level is 100%, and I have the same experience in Chrome, Edge and Firefox.
Here's an example, notice the green "joining game" text.
Large text example: https://1drv.ms/u/s!ApEMOZAE9O6wgY4OaaC2qqdA8f_gDg?e=ewzGw7 (https://1drv.ms/u/s!ApEMOZAE9O6wgY4OaaC2qqdA8f_gDg?e=ewzGw7)
The game log is similarly sized during game play, as are some buttons (Undo, for example).
[modified by Ingix to have the link working]
Are you using this on a tablet/mobile in portrait mode (long edges to the side, short ones on top and bottom)?
It looks similar in my (windows desktop) browser if I change the window size to have a portrait aspect ratio.
I was on a Surface Studio, with a display resolution of 4500 x 3000 w/ 200% scaling.
It is a touch device, but I only used keyboard and mouse. My friend, who had the same issue, was on an Apple laptop.
However, I just checked again, and the problem is gone! I confirmed it on a second machine as well. It feels like there was perhaps a CSS file/rule that wasn't getting applied, or was stuck in my cache perhaps?