Looking for confirmation to my question

So a computer reads HTML (also CSS) and JavaScript from top to bottom and left to right, meaning it’s best to write code with that in mind?

not always true
as for css selector some selector has higher precedence over other dispite they come late in code

and browser convert the html and css to dom tree

for left to right some operation has also higher precende and even work right to left

just stick that html for structure the page and css for looking and js for action

hope that help and have a nice day