Accounts are local to each instance. There is nothing stopping you from creating the user account, “dabu” at multiple instances, but there is little point in doing so. They are independent of each other, and currently, there is no concept of karma within the platform.

Your lemmy.world account can be used to post/reply on other instances (lemmy.ml, beehaw.org, etc.), and you can subscribe to communities on any other available instance so long as that particular instance is not blocked by your home instance.

It’s amazing how something as simple as changing the color of a separator can make a world of difference in how an app feels. All of these changes look great!