Many website owners have recently received an email from Google with the title, "Googlebot cannot access CSS and JS files".
It doesn't matter whether you're running WordPress, Drupal, Joomla or another platform entirely. Google has sent these emails to 100,000's of sites.
I'm going explain the issue that Google is complaining and how you can resolve it.
What is the email that Google is sending out?
Google Webmaster Tools has been sending out this notification to sites:
Here's what the email looks like:
What does the message mean?
This message is all about Google's new focus on responsive design.
Google now needs these files to test your site for mobile friendliness. Without them, your ranking will go down. We covered almost exactly the same problem back in April during Google's "Mobile Armageddon".
What is the solution?
Go to Google's Mobile-Friendly Test and check your site. Here's a screenshot of a site that's received Google's e-mail.
Thankfully, Google's tester is very informative and points out the exact issue for this particular site. It's that the robots.txt file is blocking Google from accessing the resources it needs.
You can find the exact resources that are blocked by Google by clicking on the "Show resources" link on the right-hand-side of Google's tester Compare the files there to your robots.txt to determine what needs unblocking.
Test your site again
After saving your robots.txt file, go back to Google's tester and run another test. If Google shows that your site is mobile-friendly, you've likely fixed the problem.