Images aren't stretched locally, but stretched when deployed? (CSS/HTML only)

I have a super simple webpage consisting of purely HTML/CSS. All works fine, as expected, when I run it locally.

However, when I deploy it (using Droppages, a static-page hosting platform through Dropbox), all of my images appear stretched.

I've tried several image sizing mechanisms -- setting image size in HTML (tried both percentages and specific pixel sizes), as well as setting image size in CSS (percentages and pixel sizes). All options work properly locally; none work once it's deployed.

Is this likely an issue with Droppages, or am I somehow sizing images wrong -- is it common for images to size properly locally and not elsewhere? Any workarounds you recommend I try? Thanks.