The prefers-contrast media query is even better for accessibility [1]. It allows checking if the OS is in high contrast mode and adjust the colors appropriately.
I think the idea is to replace the Microsoft's proprietary -ms-high-contrast media query [2]. It means that prefers-contrast will work in Mac and Windows. Unfortunately, Safari Technology Preview 68 doesn't seem to implement it.
That doesn’t always work though. Some people need to adjust their colours for lower contrast, for example: https://accessibility.blog.gov.uk/2016/05/26/accessibility-a... . Ideally sites would also work properly if the user changes the foreground and background colours to suit their needs.
I think the idea is to replace the Microsoft's proprietary -ms-high-contrast media query [2]. It means that prefers-contrast will work in Mac and Windows. Unfortunately, Safari Technology Preview 68 doesn't seem to implement it.
[1] https://drafts.csswg.org/mediaqueries-5/#prefers-contrast
[2] https://msdn.microsoft.com/library/Hh771830