Chrome Says mixed content but the protocols actually match

I have a web admin panel that calls the main website's jquery and style.css files. The links are loaded over https but chrome insists that it is loaded over http. I can even see the file links on "Elements" tab on the console which are in correct form (seen as https).

Below the screenshots of the content links from the "Elements" tab on chrome

And the error on "Console" tab on chrome

I have other content loading from the website which work fine. Just these two files are the trouble.
I am sure the content is available over https and the automatic HTTPS redirection works.

Important note: I am loading this content inside an <iframe> element

How can I resolve this issue?

Solution

My coworker found a solution for this. Adding <meta http-equiv="Content-Security-Policy" content="upgrade-insecure-requests"> inside of the <head> of the <iframe> seemed to solve the issue.