around this issue First of all, I know that what I'm trying to do here is bad practice, but I dont really have much choice, so please don't answer with "make the page responsive" etc.. , As per OP's request. Modify your meta tag to this
Responsive Design: max-device-width, max-width and min-device-pixel-ratio
should help you out Hidpi only means that 1 css pixel is rendered with 3x3 actual pixels (this varies for devices, iPhone pixel density is 2- so on iPhone 1 css pixel is made from 4 actual LCD pixels.). Websites on galaxy s4 are still rendered as 360x640px with pixel density 3, so you don't need any additional css for HiDPI devices. you only need to add this meta tag in year head section
it should still fix some issue You're using flexbox on the image's parent in order to center the image which is going to affect scaling. The default property for flex-shrink will prevent the image from being wider than the container. Add flex-shrink: 0 to the image. This will still allow the centering to take place but without limiting the size of the image.