How to achieve a very smooth native like scrolling on mobile browser?

I have exhausted all my CSS and javascript knowledge and I still could not figure out how they optimize their mobile website so much that it scrolls like a native app, even with images and videos that are occupying most of the viewport, it still scrolls very smooth.

I have tried

scroll-behavior: smooth;

in my CSS containers

and javascript

document.querySelector(target).scrollIntoView({ behavior: 'smooth' });

and I have even tried

will-change: transform;

attribute on a parent container that transforms content upwards computed by javascript. That is probably the worst performing one in my test.

How does facebook do it?