You can do something similar to style QToolTip in general.
QToolTip { color: #fff; background-color: #000; border: none; }
If you need the QToolTips style specifically, based on their parent widget, you can use the following syntax:
ParentWidgetName QToolTip { color: #333; background-color: #1c1c1c; border: none; }
Reading this will help you further.
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