For future questions, this is the wrong forum for questions about your own project:
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It's easiest if you use Web Inspector, Firebug, etc. Then you can see how any element gets it's styling.
And/or take a look at the supplied CSS.
Starting with 1.4, (I see you are using 1.3, though) there is also fairly good documentation on the CSS structure which I'd urge you to read. (But if you read the 1.4 docs it will be quite wrong for 1.3!)
I have a feeling the spacing you want to remove isn't actually on .ui-content. This look suspicious, but it's from 1.4, and haven't looked at 1.3:
- .ui-popup-container .ui-content > p,
- .ui-popup-container .ui-content > h1,
- .ui-popup-container .ui-content > h2,
- .ui-popup-container .ui-content > h3,
- .ui-popup-container .ui-content > h4,
- .ui-popup-container .ui-content > h5,
- .ui-popup-container .ui-content > h6 {
- margin: .5em 0;
- }