Hi,
At least when I visit this site,
- the sidebar is jammed against the topic list,
- the sidebar has the same background color as the topic list, and
- the scrollbar is pretty faint, so there’s hardly any separator between them.
So any paging down, let alone scrolling, can trigger “smooth” motion sickness.
If there’s excess window space, I’d suggest putting half that space between the sidebar and the topic list, and unless using high-contrast themes, either different background colors for the sidebar and the topic list, or a different background color for a spacer between them. Maybe the spacer and the outer edges could use the same blue as the header.