What is it?
This will check if all resources are loaded over a secure HTTPS connection. Mixed content occurs when initial HTML is loaded over a secure HTTPS connection, but other resources (such as images, videos, stylesheets, scripts) are loaded over an insecure HTTP connection. This is called mixed content because both HTTP and HTTPS content are being loaded to display the same page, and the initial request was secure over HTTPS. Browsers may block mixed content, so fixing this issue helps ensure your content loads as intended.