Jetpack’s Custom CSS Editor also gets a major overhaul for this release. The editing experience is now more streamlined and supports Sass and LESS as alternatives to traditional CSS. Write your site’s styles in your preferred language, and Jetpack handles the rest.
Those are the highlights, but this release also fixes many other issues you reported. For a complete list of changes, see the official Jetpack Changelog.
The update will be available in your WordPress dashboard shortly. Alternatively, you can always download the latest version of Jetpack here at jetpack.me.