Today I upgraded a Wodpress theme for client website. But after the upgrade got a warning for Mixed Content as shown below in web browser’s error console.

Mixed Content: The page at 'https://www.sitename.com/' was loaded over HTTPS, but requested an insecure stylesheet 'http://fonts.googleapis.com/css?family=Lato:300,400,700'. This request has been blocked; the content must be served over HTTPS.

Here is the steps I followed to fix the issue

Added theme files to Git

git init
git add .

Then searched for google font

 git grep google

Here is output

wp-organic-new/assets/css/default.css:@import url(http://fonts.googleapis.com/css?family=Lato:300,400,700);

Then I edited the default.css and updated the google font url with https