When you're working in the Pen Editor, you have complete access to both all the files you've uploaded (Asset Hosting is a PRO feature) as well as a slew of free design resources we make available to you.
Click that Assets button in the footer, and the Assets modal will pop up. We've just redesigned this area to be more useful and more in-line with other areas of the site, like our recently redesigned Pen Settings.
The biggest bit of feedback we were working from is that, for PRO members, it was too hard to access your own files. In fact, in some screen sizes and configurations, the Your Files section could have been totally off-screen and it wasn't obvious you could scroll to it. In this new design, Your Files is front-and-center when you open the modal, and all the other free resources are still there and easy to click over to.
Let us know if you have any feedback!