In the "2017 source code editor" (I think that's what it's called - the one that works with VisualEditor), sometimes when typing in text that goes towards the edge of the screen, the text near the end of each line gets a bit 'fuzzy' with what looks like a misaligned shadow. Here's a screenshot of one example.
I'm on macOS 10.13.5, and this screenshot was taken in Firefox Developer Edition 61, but I've also had this issue in the latest stable Chrome. Thanks!