If I understand you correctly.
there are two css settings for the hover tool tip
Control Panel » Styles » Edit or Add a Style
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Misc. Properties
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popup_content_header
popup_content
Some times using the copy link to the right of the property will fix it.

BTW this is one of the enhancements added later on in the 7.x series so older styles will not have a setting for them.

Blue Man Group
There is no such thing as stupid questions. Just stupid answers