That's a strange question. There is no need for a site to be compatible with the OS on the machine where the "user agent" (=browser) runs.
All that matters if it displays correctly in the browser used. Generally, that's acceptable if https://validator.w3c.org doesn't show any errors.
I checked in Firefox 50.1.0 in Windows 10, and the home page looked OK, although I couldn't read it, because it was in Arabic. And it looked the same in Edge (and that's specific for Windows 10).
Is my[site is compatible with Windows 10
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