You can get pretty far in making a slider with just HTML and CSS

A "slider", as in, a bunch of boxes set in a row that you can navigate between. You know what a slider is. There are loads of features you may want in a slider. Just as one example, you might want the slider to be swiped or scrolled. Or, you might not want that, and to have the slider only respond to click or tappable buttons that navigate to slides. Or you might want both. Or you might want to combine all that with autoplay.

I'm gonna go ahead and say that sliders are complicated enough of a UI component that it's use JavaScript territory. Flickity being a fine example. I'd also say that you can get pretty far with a nice looking functional slider with HTML and CSS alone. Starting that way makes the JavaScript easier and, dare I say, a decent example of progressive enhancement.