code: def highlight_current_line(self):
          
          selection = TextDecoration(self.textCursor())
          selection.format.setProperty(QTextFormat.FullWidthSelection,
                                       to_qvariant(True))
          selection.format.setBackground(self.currentline_color)
          selection.cursor.clearSelection()
          self.set_extra_selections('current_line', [selection])
          self.update_extra_selections()
docs: Highlight current line