title: net::ERR_INSECURE_RESPONSE with CDN
body: <p>I have deployed an app on heroku but the css is not working.</p>
  
  <p>I am using the w3.css framework and I am importing it like this:
  <code>&lt;link rel="stylesheet" href="//www.w3schools.com/lib/w3.css"&gt;</code></p>
  
  <p>The error I am getting is:
  <code>GET https://www.w3schools.com/lib/w3.css net::ERR_INSECURE_RESPONSE</code></p>
  
  <p>I am pretty sure that it is related to the certificate of the site.</p>
  
  <p>But even when I manually accept the "invalid" certificate in the site, I get a 404 error.</p>
  
  <p>Also, from what I see, w3.css only offers its CDN through http:
  <code>http://www.w3schools.com/lib/w3.css</code>
  not https:
  <code>www.w3schools.com/lib/w3.css</code></p>
  
  <p>So, I just wanted to confirm that this is actually the case and that it is not my fault (not knowing how to load sth over https!)</p>
  
  <p>Finally, it's not a Chrome error (from what I've read around in SO).
  Firefox doesn't work either.</p>
  
  <h2>UPDATE</h2>
  
  <p>Just to inform that, as expected, the error was resolved when I downloaded the w3css framework and linked to it locally.</p>