You shouldn’t block Googlebots’s access to your CSS or JS files.
We’ve known that for a long time, but more recently we’ve had reminders from around the community and Google themselves because of algorithm updates and proposed changes to the way mobile sites might be ranked in mobile search.
Some of us might be assuming that CDN’s serve our content in precisely the way we’d like. Not necessarily so, not for search engines at least.
We need to check what, if any, resources we’ve blocked in case the restriction is unintentional.
Here’s how the tool looks;
And immediately it’s clear we’ve been serving something from a CDN that’s blocking Googlebot.
The files in question:
<link href="https://vjs.zencdn.net/4.5/video-js.css" rel="stylesheet">
Which are, of course, easily updated to local files (or a CDN of your choice, but we'll get to why I chose local in a moment):
<link href="http://builtvisible.com/wp-content/themes/gadg3t/css/video-js.css" rel="stylesheet">
I've chosen just to host those two files locally because we're running on WPEngine. Their service automatically serves JS and CSS via their CDN, so now in our page, you'll see:
<link href="http://36bvmt283fg61unuud3h7qua.wpengine.netdna-cdn.com/wp-content/themes/gadg3t/css/video-js.css" rel="stylesheet">
So that's a terrific little nudge from Google to remind us to check the accessibility of our externally hosted files. Pretty cool.