Too much vertical spacing in sidebar

There’s a ridiculous amount of margin/padding above and below the headings of sidebar widgets and the widget contents, such that even on a full-size screen, you can really only see one widget and part of the second one. I know I can adjust it with custom CSS, but the need to do that means I can’t really recommend the theme to my clients, who need things simple. Please provide a more reasonable default, or give us an official way to adjust it — preferably both.