Is it only my opinion or this new desktop version is extremely similar to Airbnb website? :P

You are lucky because you already know a tool to design and manipulate UI but I think that the difficult part is to improve your aesthetic sense and to study some basic rules of a good style guide.

I want to suggest you to give a look to https://designcode.io . It's about Sketch (a UI oriented manipulating tool) and about iOS app, but it's also about how to use colors, text, font, etc.

I have seen Teehanlax's GUI in past and I use them a lot when I design app in Photoshop, but previous versions weren't so complete. Thank you for your tip!