To date, we've used a singular font stack for all browsers and OSes. Across the board, none of the fonts currently in use are the (preferred and well designed) system fonts. This PR drops the old font stack for a new native system-based one. Essentially, every OS will have it's own font-family with this new stack.
As an example, on OS X (Safari, Chrome, and Firefox) and iOS, the font will now be Apple's San Francisco. On the latest versions of Windows, it'll be Segoe UI. On Linux, well, you get whatever flavor of Linux you get
I took a quick look at our buttons as an example (as they tend to give us the most trouble) on Win7 IE9 and Win8 IE11 and things look a tad out of alignment in IE9. IE11 looks just dandy.
For full details on what font is shown where, please head to https://www.smashingmagazine.com/2015/11/using-system-ui-fonts-practical-guide/#details-of-approach-b.
Overall, I'm pretty stoked about this. Would love to hear what others are thinking.
Sources: