Thanks for asking.
Pro and X Theme: Apart from header and footer builder, Pro theme comes with design cloud. In version X Pro version 2.2.0 we have also launched Drag and Drop feature in header and footer builder along with inline editing (also available in Cornerstone). Version 2.2.0 also comes with skeleton mode in header and footer builder. I am sharing relevant resources that you can take a look for more information.
Design Cloud: Unlike X Theme wherein you have the ability to import demo contents in Pro Theme you don't have that option. Reason begin Pro Theme uses a different templating system. To solve this we have launched Design Cloud. More information on design cloud can be found here.
Here is a tutorial on how to use Pro Theme design cloud:
Pro version 2.2.0: This version comes with the option to inline editing, drag and drop for header and footer builder, skeleton mode for header and footer builder. More information can be found in changelog.
CSS customisation: Absolutely, you can customize Pro Theme using CSS. However, with the host of features and tools that Pro theme comes with in a very rare scenario you will have to write Custom CSS. However, as website requirement changes there is no limit to the level of customization that's possible with Pro Theme that includes CSS and GUI tools.
I would encourage you to take a look at the KB section as new articles and resources are constantly bing added. It will help you to get most out of Pro Theme.
If you would like to learn CSS, I am sharing few resources that you take a look to get started with CSS and an interesting tool that you can use to speed up the development process.
I recommend you to watch following video that will help you to get started with CSS.
Sometimes it can get a bit difficult to find out the right selector to be able to write the required CSS codes. A handy tool that can help you in this is Google Chrome dev tools. I am sharing the resource that you can refer to get started with dev tools.