The styling of the annotation selection and control points have been updated in version 7.3. The main updates are:

• When an annotation is too small, there will be some extra padding given, so it can be selected easily.
• The selection lines are no longer dashed
• The Control Points outline style has been changed from dashed line to solid line
• The Control Points outline color has been changed from #418cfc to #3183c8
• The Control Handle has been updated from the white circle to a blue circle
• There is a small shadow given to Control Handles

If you want to use the selection style from version 7.2 and earlier, you can update the following properties:

WebViewer(...)
    .then(function(instance) {
      const { Annotations } = instance;

      // selection model outline adjustment
      Annotations.SelectionModel.useDashedLine = true;
      Annotations.SelectionModel.selectionOutlineThickness = 2;
      Annotations.SelectionModel.defaultSelectionOutlineColor = new Annotations.Color(65, 140, 252);
      
      // control handle adjustment
      Annotations.ControlHandle.handleWidth = 12;
      Annotations.ControlHandle.handleHeight = 12;
      Annotations.ControlHandle.color = new Annotations.Color(255, 255, 255);;
      Annotations.ControlHandle.outlineColor = new Annotations.Color(65, 140, 252);

      // do not show extra padding when selected annotation is too small
      Annotations.SelectionModel.selectionOutlineExtraPadding = 0;
  });