Mark S is correct, the fonts are in Control Panel (font-family for view mode, code for code, editor for edit mode)
font-family
-apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol"
code
"SFMono-Regular",Consolas,"Liberation Mono",Menlo,Courier,monospace
editor
(none listed)