Wes Bos, a web developer, writes about JavaScript, CSS and tooling, and sells and gives away web development courses.
Commenters often recommend his JavaScript, React, flexbox and grid courses for beginners and praise his regional pricing for countries with lower purchasing power.
Looking at the screenshots and the CSS in question, and presuming that before it just wasn’t specifying fonts at all, I prefer the “before” result if I’m the consumer, mostly because I like the fonts I set in my browser, and consider Inter and Incosolata a slight regression. Also most of the other styles I disagree with; capping the width and reducing the line-height for headings is about all I actually agree with in there.
But really I think that if this is all you want to change with org-mode HTML output, it must export pretty decent HTML. (I’m not familiar with it.)
(Analysis of the things I particularly don’t like: 1.6 is too large a line-height; I prefer #000 to #444, though I’d settle for #222; image should use max-width instead of width, and have height: auto added, and what’s with the 700px instead of 900px, especially if you’re not going to block and centre it?; border-radius on images seems a bad idea; I dislike gratuitous fiddling with ::selection colours—only touch it if you have actual brand colours that you’re making it align with, like https://wesbos.com/, and be cautious even in that, as is demonstrated in the .highlight on that page which thwarts selection styling.)
I'm personally a big fan of Frontend Masters: https://frontendmasters.com. I've found it to be one of the most comprehensive resources for web development out there, especially for front-end work. I think it's a great starting point for any prospective web dev, especially if you're keen on learning some crucial JS concepts.
Once you dive a bit into the fundamentals, you can also check out Wes Bos's suite of courses: https://wesbos.com/courses/. His React tutorial is definitely my favorite one out there.
https://developer.mozilla.org/en-US/docs/Web
Follow following Youtube channels:
1. FreeCodeCamp: https://www.youtube.com/channel/UC8butISFwT-Wl7EV0hUK0BQ
2. The New Boston : https://www.youtube.com/user/thenewboston/featured
3. Ben Award : https://www.youtube.com/user/99baddawg/featured
Outside Youtube:
1. Wes Bos : https://wesbos.com/
2. Udemy : https://www.udemy.com/understand-javascript/
3. CSS Tricks: https://css-tricks.com/
4. Egghead: http://egghead.io
Etc etc
As one person living in one of those countries with greatly reduced purchase power, I really appreciate the way Wes Bos[1] has done it for his courses (I've bought a couple of them).
He's got an episode on his podcast on how he implemented it [2].
It does sound like some work and I'm not saying you should discount or give away your work though.
[1]https://wesbos.com/
[2] https://syntax.fm/show/233/hasty-treat-purchasing-power-parity
All of the following cost money but are good:
Wes Bos (https://wesbos.com/courses/) and Scott Talinksi (https://www.leveluptutorials.com/) have some great modern JavaScript courses, most of which require understanding of coding and the basics of web dev.
For everything else Pluralsight (https://pluralsight.com) is pretty comprehensive.
I've been doing his React course and it's been very helpful so far. I have no reason to believe his other course aren't just as good:
http://wesbos.com/courses/
NOTE: Some of his courses are paid. The plain JS course is free though. However, I paid for the React course and feel it was very worth it.