call to google fonts in http

Hi,

  My webiste is in https.

  there is a mixed-content error, because the call to google fonts is made over HTTP and not HTTPS, in the file /sites/default/files/drupalexp/zap/css/style-[*].css

  If I change it directly in the css file, it's ok, but this file is regenerated every time I change something in the "appearance" menu, so my change is erased.

  Can you tell me which file I need to edit to switch this call to HTTPS, permanently ?

  Thank you !