font: caption;

Joe Richardson shared this little trick over on CodePen:

body {
   /* operating system font  */  
   font: caption;
}
  • If you're on Ubuntu this will be the Ubuntu Font.
  • If you're on Yosemite this will be Helvetica.
  • If you're on El Capitan this will be San Francisco.
  • If you're on Microsoft this will be Segoe UI.

Not entirely sure the support of this, but if it works for your needs it's a lot easier than declaring them directly or sussing it out with JavaScript.

Update: Viljami Salminen has done a lot more testing on this and it looks like there are a few problems in iOS. Make sure to check out his Pen for more info.

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