@import url("a.css"); files get ignored

[mikeytown2]

If you want to take this to the extreme make a webpage that uses this style for loading css

<style type="text/css" media="all">
@import url("a.css");
@import url("b.css");
@import url("c.css");
@import url("d.css");
@import url("e.css");
</style>

When running critical https://import.css.url.com/ it'll spit out this "Error: css should not be empty" even though css files do exist.

[bezoerb]

Inline styles are currently not processed by critical so these imports are invisible to critical.
You could work around this by specifying the imported stylesheets in the options like this:

critical.generate({
  css: ['a.css', 'b.css', ...]
});

Even though inline-critical won't process the inline styles either so you would end up with the critical css inlined alongside the inline styles with the @import statements ;)

Why don't you use <link rel="stylesheet"> tags?

[mikeytown2]

import can in in the CSS as well; this syntax just makes testing it a lot easier. What file would I need to edit in order to do a pull request for this feature? Could you point me the right direction?

[bezoerb]

The stylesheets are extracted with oust
You can find this in lib/core.js.
The critical css is inlined with inline-critical. So if you like you can prepare a PR on these two packages.