mixed content: the page at '<url>' was loaded over https, but requested an insecure stylesheet '<url>'. this request has been blocked; the content must be served over https
This often happens when certain assets like css or javascript files are loaded using
http instead of https. It is also very often the same case for images, fonts and icons.
Typically speaking, many CMS systems have "plugins/extensions/apps" that can sort out
mixed content warings relatively painlessly, however, occationally you may find that
you work with bespoke websites lie myself. In these cases, try to use "inspect element"
with Google Chrome, or Firefox's "firebug" to check for any instances of "http://" in the
source code of the website's page that gives you the warning/s. This should point you in
the right direction regarding which file paths to update in-order-to clear up that mixed
content error.
Best of luck, I know that this particular issue can be frustrating at times.