Borders and white space. Funny how much of modern clean design aesthetic was already possible to do with basic HTML back in the day but we were too fascinated with blinky flashy colorful tags to ask ourselves "Doesn't this altogether look like neon hell?"
We had to design websites in high school, circa 7-8 years ago. Pretty sure if anyone had implemented a flat desing they would have been given a D for poor effort.
It's all about that terrible blue button in Dreamweaver that animated concentric circles when you hovered over it..
Section? Sounds like something with a header? I would probably just wrap the section in a section tag.
Not necessarily. A horizontal rule (or flourish) is often used in fiction as a context-shift indicator within a chapter. Technical documents are not the only documents.