How to use the babylonjs-gui.Control.VERTICAL_ALIGNMENT_CENTER function in babylonjs-gui

pipeline.depthOfField.fStop = 3;
  pipeline.depthOfField.focusDistance = 2250;
  var moveFocusDistance = true;

  //add UI to adjust pipeline.depthOfField.fStop, kernelSize, focusDistance, focalLength
  var bgCamera = new ArcRotateCamera("BGCamera", Math.PI / 2 + Math.PI / 7, Math.PI / 2, 100,
      new Vector3(0, 20, 0),
      scene);
  bgCamera.layerMask = 0x10000000;
  var advancedTexture = AdvancedDynamicTexture.CreateFullscreenUI("UI");
  advancedTexture.layer.layerMask = 0x10000000;
  var UiPanel = new StackPanel();
  UiPanel.width = "220px";
  UiPanel.fontSize = "14px";
  UiPanel.horizontalAlignment = Control.HORIZONTAL_ALIGNMENT_RIGHT;
  UiPanel.verticalAlignment = Control.VERTICAL_ALIGNMENT_CENTER;
  advancedTexture.addControl(UiPanel);
  var params = [
      {name: "fStop", min:1.4,max:32},
      {name: "focusDistance", min:0,max:5000},
      {name: "focalLength", min:0,max:500}
  ]
  params.forEach(function(param){
      var header = new TextBlock();
      header.text = param.name+":"+pipeline.depthOfField[param.name].toFixed(2);
      header.height = "40px";
      header.color = "black";
      header.textHorizontalAlignment = Control.HORIZONTAL_ALIGNMENT_LEFT;
      header.paddingTop = "10px";
      UiPanel.addControl(header); 
      var slider = new Slider();
      slider.horizontalAlignment = Control.HORIZONTAL_ALIGNMENT_LEFT;