Flutter delegates the drawing to Skia, instead of delegating it to iOS or Android native widgets.
Skia is similar to Cocoa native controls, which are drawn by Quartz.
Flutter also reimplements all of the behaviors of the built in controls.
Flutter lets you build modern mobile, web, desktop and embedded apps with productive live Hot Reload. It's fast at development and runtime which can be run in a JIT VM, as AOT compiled or transpiled to tree-shaken JS.