Do we want the legend to be vertical for all chart types? This makes sense for pie charts but think it would constrain the space available for line and bar charts quite a bit, especially on the smaller mobile charts.

^ @DTorsani-WMF

Good question. I think as long as we can make wrapping for horizontal layouts work well and respond to pushing a chart down as a legend wraps to more lines, I think we can prioritize using horizontal legends for all charts other than pie.

IIUC, the legend still needs some fixes for dark mode, at least in Line Charts, when the quantity of entries requires showing the arrows-to-scroll feature.
E.g. in https://www.mediawiki.org/wiki/Extension:Chart#Line