Ask HN: Web Design to Webdev Handoff

tl;dr How does the web designer to web developer handoff work? How did we get here? What are best practices?

I'm mainly a systems/backend developer but recently I've become more interested in web design. Today, I decided start learning a UI design tool and picked Figma. An amazing app. I had no trouble creating an initial design, and then I went to export ... PNG/SVG/PDF? No HTML, CSS?! It has CSS for elements, but not for many parts of the design (e.g. layout constraints). How is this supposed to work? Web developers just recreate the design in code largely from scratch? Is this the state of the art for the web designer to web developer handoff? If I'm working on a small-scale project (e.g. just me) is there any reason I shouldn't just use HTML/CSS/JS directly?