Options:
There are others, of course.
The last option is most flexible. At first it doesn't seem feasible, but actually with the Svelte component approach it's possible. There are examples floating around the web.
Pancake is Rich Harris's approach, and it looks nice, although I'm not sure has time to keep it maintained. Keep an eye on it.
D3 and Vega/Vega-Lite are both powerful and well-known. D3 seems the most powerful, though I'm no expert. In either case, they are not really taking advantage of Svelte's approach, and might be a little bloated. Regardless, I am leaning towards Vega/Vega-Lite just so I can quickly get some prototype visualizations together.
Charts.css looks awesome, and I think theoretically it's the optimal approach. My only concern is getting interactivity, which I would really like.