Chrome, Firefox and newer versions of Internet Explorer enforce the Cross-Origin Resource Sharing standard, and thus only render web fonts served with the appropriate Access-Control-Allow-Origin response header. As we use Google Fonts that may be viewed on any domain, the fonts are served with the following response header:
Access-Control-Allow-Origin: *You might have a proxy server in your network that strips the header Access-Control-Allow-Origin from the response, after which the browser will not render the fonts.
Configure the proxy to not strip this header.
With Chrome, check for the relevant warning message in the DevTools console.