A common need or question when you upgrade your application from VB6, Windows Forms or Powerbuilder is: Where is the designer?
On Modern Web Architectures the user interface is implemented on a FrontEnd project usually in Angular or React and normally those projects do not provide a visual designer experience.
However you can use the Angular Playground as an alternative. It won't be designer as you are used too but it will allow you to preview your screens without running or compiling the backend and you can also make small changes and see inmediatly how the look.
I created a small video to show how this works: