[RumourRider]

You need to think about what the browser is actually doing when it displays a web page. You need to think about what happens when you type the URL in and what the browser is doing conceptually.

If you have any experience programming 2D graphics with SDL this will help you to understand what is happening as well.

There is an old school talk by Nikolas Zakas on JavaScript Performance from 2009 which while some of it is out of date now due to improvements in Browser engines, the fundamental ideas are still the same.

https://www.youtube.com/watch?v=mHtdZgou0qU

If you skip to the 35 minute mark he speaks about reflow specifically. Generally I still use many of these techniques when writing vanilla JS (which is unfortunately rare these days). There are other talks where he talks about many other performance specific topics.

Obviously none of this is as good as real world experience of dealing with a thorny issue.

[troupo]

> If you have any experience programming 2D graphics with SDL this will help you to understand what is happening as well.

No. No it will not. Nothing in 2D graphics will help you understand things like "simple animation required full layout re-calculation and re-painting of the entire page"

[RumourRider]

Yes it will. Most of the CSS styling is literally wrappers around draw calls.