How would you design an offline-first data layer using IndexedDB with background sync — including conflict resolution when the client reconnects after hours offline?

Imagine you have a notebook where you write down your drawings, but sometimes you lose your crayons. IndexedDB is like a magic notebook that saves your drawings even when you're not connected to the internet. When you get your crayons back, the notebook checks if your new drawings match what's already in the big class notebook, and if there's a difference, it asks a teacher to help decide which one to keep.