code: def set(self, class_name, state, key, value):
          
          self._styles.setdefault(class_name, {}).setdefault(state, {})
          self._styles[class_name][state][key] = value
docs: Set a single style value for a view class and state.
  
          class_name
  
              The name of the class to be styled; do not
              include the package name; e.g. 'Button'.
  
          state
  
              The name of the state to be stylized. One of the
              following: 'normal', 'focused', 'selected', 'disabled'
              is common.
  
          key
  
              The style attribute name; e.g. 'background_color'.
  
          value
  
              The value of the style attribute; colors are either
              a 3-tuple for RGB, a 4-tuple for RGBA, or a pair
              thereof for a linear gradient.