I feel like an idiot here. I’ve more than proficient in HTML, CSS, and Javascript (been professionally doing front-end development for decades), but I’m starting to get asked to build HTML5 ads and I can’t for the life of me find any resources that aren’t pushing me to some specific GUI-based solution.

Am I completely wrong in my assumption that an “HTML5 ad” is just HTML/CSS/JS?

Does anybody know of any good guides for getting started with HTML5 ads if you already know HTML/CSS/JS?