Random grid gotcha that drove me crazy some time ago: due to browser bugs we can't use <img> elements with percentage widths or heights as grid items. The grid cell dimensions get blown out to the ones of the original image. Seen in both Firefox and Chromium. Relevant FF bug is probably https://bugzilla.mozilla.org/show_bug.cgi?id=1857365 '<img> grid item with percentage height, "width: auto", "grid-template-columns: auto", and no track stretching makes column to have the same width of the original image's width' (although someone there claims it works in Chromium).

so if the img has a specific size set in width and height attributes or via css, and that size is not percentile or auto, the problem doesn't exist?

I'm just confused by the "original image's width".