System Fonts use a local font stack

font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol"
font-family: system-ui, -apple-system, BlinkMacSystemFont, Segoe UI", "Roboto", "Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif;

Serif Fonts all characters have stroke endings

font-family: Georgia, serif;
font-family: "Times New Roman", Times, serif;

Sans-Serif Fonts no character has stroke endings

font-family: Arial, Helvetica, sans-serif;

Monospace Fonts all characters have the same width

font-family: "Courier New", Courier, monospace;