Thanks for trying it out! Although the game is made to work only with 16:9, the letters are still supposed to be in their respective positions. Thanks for noting it.
Viewing post in Lily the Philosopher jam comments
Just to be clear, I meant letterboxing as in the extra pixels on the top and bottom that try to keep it in 16:9 ratio. Another thing I found out: when in 16:10 the hotspot for mouse-to-button on the main menu is offset, which is probably all related. Didn't notice before since I moved it to my standard monitor and played with it for minute.

Sorry my bad. In that case it works as intended (the grey area should be on the top while the game area should stick to the bottom). For the mouse, I made some tests before for such cases and it seemed to be working for different window sizes. I guess I will have to do more tests. Thank you again for clarifying the issues!