Thanks for letting me know!

It's a graphical error that sometimes happens on larger screens. It doesn't seem to happen on my Macbook with this particular image, but I have seen it happen on 1920x1080. My best guess would be that the image doesn't have the correct dimensions (too wide compared to how tall it is, for example) and the webpage doesn't know what to do with that. It's an issue I've seen happen with other images I tried, and unfortunately I don't know how to fix that :c

The best way around it is to choose an image that doesn't have this issue and test it out beforehand! You could also ask the HTML forums, as I'm sure someone more qualified than I will know the exact answer ;v;