.htmlfile that wasn't just
<slot> tag required some Stack Overflow searches and some solutions that I'm still not sure I grok.
If there was ever a chance we were moving away from doing everything in React I'd jump to web components in a second, but when we are building everything in React, adding in another compiler feels like it's overcomplicating our development tooling. But maybe I'll regret saying that when we switch to Vue and have to build another carousel.
I put the demo up on GitHub, it's probably broken in IE. I hate carousels.