OpenLayers 5: add Interaction and style selected feature

Question

based on this example addInteraction adds opacity, so I am setting a new style for each selected feature, however the clicked features remain red.

I only want to style with the red border only one feature at a time.

var style_simple = new ol.style.Style({
  fill: new ol.style.Fill({
    color: 'khaki'
  }),
   stroke: new ol.style.Stroke({
      color: '#880000',
      width: 2,
      opacity:1
    })
});

var style_noBG = new ol.style.Style({
    fill: new ol.style.Fill({
    color: '#5755d900'
  }),
   stroke: new ol.style.Stroke({
      color: 'yellow',
      width: 2,
      opacity:1
    })
});
    var style_selected = new ol.style.Style({ //style to be added on selected layer
        fill: new ol.style.Fill({
        color: '#5fba6a38'
      }),
       stroke: new ol.style.Stroke({
          color: 'red',
          width: 3,
          opacity:1
        })
    });

    var getStyle = style_simple;
    $("#layerbg").change(function () { //fires when checkbox is changed
      if ($(this).is(':checked')){
        getStyle = style_simple;
      }
      else{
        getStyle = style_noBG;
      }
    vector.setStyle(getStyle);
    });

    var vector = new ol.layer.Vector({
      style:style_simple,//set default style when page is loaded
      source: new ol.source.Vector({
        //url: 'https://openlayers.org/en/latest/examples/data/geojson/countries.geojson',
        url: 'JS/getjson.json',
        format: new ol.format.GeoJSON()
       //,serverType: 'geoserver'
      }),opacity: 1
    });

var selectClick =  new ol.interaction.Select({
    condition: ol.events.condition.click
  });

        if (select !== null) {
          map.addInteraction(select);
          select.on('select', function(e) {
          var extent = e.target.getFeatures().getArray()[0].getGeometry().getExtent();
          e.target.getFeatures().getArray()[0].setStyle(style_selected); //commenting out this line works but adds opacity to the layer
          map.getView().fit(extent,{duration: 590},map.getSize());
          });
        }

Answer 1

Since your styles are on the layer specifying the selected style when you create the Select interaction should be sufficient

var select = new ol.interaction.Select({
     style: style_selected,
     ...  // any other options
});

(and remove the line which sets the style on features)