Change frame background color

I would like to change the background color of a frame (on a mouseEnter event). I have tried using

Code:

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this->setStyleSheet("background-color: red");

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but as you can see in the attached image, the formatting gets all messed up. How do I change only the background color, leaving everything else intact?

You can mention the class you want to set the stylesheet for, so that it doesnt affect other widgets.
eg. setStyleSheet(" .QFrame { background-color : red } ");