On the browser, Thank You!
Viewing post in Mr. Magpie's Harmless Card Game comments
Ah, yeah that could be it. It might also be something to do with a corrupted save file. You might want to try the downloadable version and/or try clearing your cache in your web browser for itch.io.
I know we've added a lot of unperformant things recently, we will hopefully find the time to optimize them, but even then, dramatic lighting in a web browser is a pretty hard thing to pull off.
Really appreciate the bug report though! Thanks!