System font stack allows us to:

• Boost performance
• No flash of unstyled text (FOUT)
• Native look
• Overall: better experience
• (drawback) Default fonts vary

To import system font stack:

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen,    Ubuntu, Cantarell, "Open Sans", "Helvetica Neue", sans-serif;
}