[Question] adding filter to styleManager

Hi, I am trying to add a filter property to Styles. The problem that I am having is that the property demands 2 arguments: 1. The type of filter 2. The strength. e.g filter: blur(10%). the problem I am having is that when added to the css file I am getting- filter: blur 10%. I understand that I should be using property.functionName to fix this, but cannot figure out how (there appear to be no examples of this in the existing libraries).

The code I have is:

   sm.addProperty('Extra', {
      name: 'Filter',
      property: 'filter',
      type: 'stack',
      properties: [{
        property: 'filter_type',
        type: 'select',
        defaults: 'none',
        list: [{ value: 'none' }, { value: 'blur'} ,{ value: 'brightness'},{ value: 'contrast'} ,{ value: 'drop-shadow'} ,{ value: 'grayscale'} ,{ value: 'hue-rotate'} ,{ value: 'invert'} ,{ value: 'opacity'} ,{ value: 'saturate'} ,{ value: 'sepia'} ,{ value: 'url'}],
      },{
        property: 'filter_strength',
        type: 'slider',
        name: 'Strength',
        units: ['%'],
        defaults: 100,
        step: 1,
        max: 100,
        min:0,
      }],
      functionName: () => {

      }

    });

Thank you