How to change only one attribute in PyQT6?

Question

I have the animated button. This is how I create animation:

self._animation = QtCore.QVariantAnimation(
            startValue=QtGui.QColor(self.color_light_orange),
            endValue=QtGui.QColor(self.color_dark_orange),
            valueChanged=self._on_value_changed,
            duration=150,
        )

def _on_value_changed(self, color):
    self._update_stylesheet(color)

def _update_stylesheet(self, background):
    self.setStyleSheet(#stylesheet)

The thing is everytime button hovered _update_stylesheet function called. As you can see it has background argument which is desired background to set. I know I could insert all stylesheet like this:

self.setStyleSheet(f"""
...
background-color: {background}
...
""")

But stylesheet for this button is about 20 lines and I would like to place it inside separate style.css file. The problem is that I don't know how to change only background so I could do like this:

# Set css file for the whole app
with open("style.css", "r") as f:  
    app.setSheetStyle(f.read())

... 

def _update_stylesheet(self, background):
    self.changeOnlyOneAttribute(background) # Function I would like to have

If there are another ideas to keep stylesheet separatly inside style.css tell me please!