Sorry, I think I wasn’t clear in my last post. The idea of the multi-column sidebar is only as an expandable (expanding to the right) option. You may expand it temporarily while reviewing budget spending, it would likely hover over the calendar, not shrink it. The normal view would be pretty much as it is today, with the category spending showing spending for your entire finances, not just the current account.
In fact, it just dawned on me… to make this more visually clear, the Account Tabs would start AFTER the category side bar – so the category side bar would not be specific to any account, but a global shared entity.