How to know which font is used by browser from CSS font-family list?
In order if available.
In your example it'll go for Roboto first and keep the next ("Helvetica Neue Light", "Helvetica Neue", Helvetica, Arial, "Lucida Grande", sans-serif
) as back-up, if it's available.
In firefox-developer-tools, Inspector > Fonts tab displays "Fonts used" by the currently inspected element. Edit fonts MDN
In google-chrome-devtools, Elements > Computed tab displays "rendered fonts" for the currently inspected element. "Even if its name isn’t in the font-family list." whats-that-font , Hackernoon
Firefox :-
Chrome :-
Thanks, @xuemind for suggested edit