System Font Stack
If you don’t want to use Webfonts due to size or other reasons, you can fall back to system fonts to provide an integrated experience.
This is what GitHub uses:
body {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
}