Currently, on Linux and Windows platforms, if the page is zoomed (e.g. with Ctrl + '+' or Ctrl + '-'), then the icons in placeholder images stay the same visual size instead of scaling as the content around them on the page scales.

From schenney@: "Linux and Windows use zoom to implement DPI adjustment. The fix for the problem is to apply the zoom as a scale, obtaining the value from the style on the element." https://chromium-review.googlesource.com/c/chromium/src/+/858288#message-ed7b919e7f6e762face25f1a2439cef8a425c71c

Note that this isn't a problem on Android or Mac platforms, since those platforms use compositor scale to zoom in/out which causes the icons to get visually larger/smaller appropriately.