What languages does Riot use for their web previews/events?

Hi! I've seen some of the incredible experiences Riot has made with things like the Gnar preview, Sion Reborn teaser, and the Shurima event page. I was wondering; what languages, frameworks, APIs, etc did you guys use to make them? I assumed some of the basics like HTML, CSS and Javascript could be involved, but I'm honestly not sure.