Maybe you want to use the following instead of the selector div.rendered_html (and I think we don't need the max-width).

It works locally. Yeah: locally. :)

.output_subarea.output_html.rendered_html.output_result {
  overflow-x: auto;
}

The thing is, now all wide outputs will be able to scroll. On the other hand, if we only want to target a table, we need to wrap it in a block or something. I think.

I didn't try wrapping the table in a new block or div. I just tried a couple of plots with what I suggest above, and it seems fine.