There are things that seem really complicated, and end up being really easy to implement (like importing a dozen different image file types, or auto-resizing controls inside a window).
And there are things that take a lot of work, like making sure that when you resize a window, not just the current card, but all other cards are properly resized, without looping over all cards in the stack (possibly thousands).
I'm currently working on the latter part. 😅