How to find the font on the site if it is not specified in css?

Question

css

I'm building a site, in css I specified only the sans-serif family, it doesn't show anything through firebug and google web-tools. I understand the font is taken from the css user agent? How to recognize it, otherwise I liked it :) Thank you.

Answer 1

Answer 2

https://chrome.google.com/webstore/detail/fontface...
Helps a lot in such matters