Source file: class.jetpack.phpView in GitHub
(bool) Should CSS be concatenated? Default to true.
Since: Jetpack 3.2.0
Instead of including a separate CSS file for each Jetpack feature, Jetpack enqueues only one file, built by concatenating all CSS from all Jetpack features. This limit the number of requests made when loading a site.
To deactivate this, you can use the following snippet:
add_filter( 'jetpack_implode_frontend_css', '__return_false', 99 );