docs: def parse(self):
          """
          Parses the CSS contents and returns the cleaned CSS as a string
  
          :returns: The cleaned CSS
          :rtype: str
          """
          # Build the HTML tree
          self.tree = self._build_tree(self.html_contents)
  
          # Parse the CSS contents
          self.stylesheet = self.parser.parse_stylesheet(self.css_contents)
  
          # Get the cleaned CSS contents
          self.cleaned_css = self._clean_css()