Semantic web is a bit different from semantic HTML.

As I understand it, the main point of semantic web is making the web machine readable, often using languages specifically designed for that task that are not HTML.

Semantic HTML is more concerned with writing standardized HTML that leverages browser capabilities and respects users who use assistive technology to browse the web.

Frankly, I don't see what this framework has to do with either. I was curious about how they implemented the dropdown menus, and they're specially styled <details> elements, which are normally used for accordions. That seems a bit strange to me, because the obvious choice for a dropdown is the <select> element.