CSS spec doesn't mandate specific font names, those are decided by the font creator or css author. San Francisco is Apple's new (?) font that replaced Helvetica

CSS spec doesn't mandate specific font names, those are decided by the font creator or css author. San Francisco is Apple's new (?) font that replaced Helvetica Neue. The typo might be intentional--I had to intentionally use the wrong name for a Windows system font in my @font-face stylesheet recently to ensure the browser wouldn't use the system version (fake-bold italic looked better than bold fake-italic in the headings, and I couldn't find a bold-italic version)