You are now in the realm of custom CSS. For widgets or specific sidebar areas (e.g., primary, secondary, top, bottom), it is not too difficult.
So, for example, to change the line height of the entire Primary sidebar (and just that area), open the CSS+ box on the Primary Widget Area BG option found on the “Sidebars & Layout” tab. Then enter
{line-height:1.5} (or whatever value need)
You can do this for any area with an area BG color option – it is an important intent of the CSS+ option for BG colors.
As for specific individual widgets, that is at an entirely different level. To do that, you must know the HTML ID of a specific widget. The only way to find that out is to either read the HTML of the page by right-clicking the page and selecting “View Page Source” (message varies depending on browser), and finding the <aside id=”widget-id”> tag for a specific widget area, or using a developer’s tool to examine the page content.