Why PolygonGraphics' outlineWidth property doesn't work

I use GeoJsonDataSource to load some polygon and i want to set a outlineWidth of every polygon,but the outlineWidth property of PolygonGraphics is useless,whatever the width set,it shows the same width

Cesium.GeoJsonDataSource.load('./data/data.json').then(dataSource => {
        viewer.dataSources.add(dataSource);
        var entities = dataSource.entities.values;
        entities.forEach(function(entity,index){

          entity.polygon.fill = Cesium.Color.WHITE.withAlpha(0.0001);
          entity.polygon.outline = true;
          entity.polygon.outlineColor = Cesium.Color.YELLOW;
          entity.polygon.outlineWidth = 50;
        });
      });