When it comes to web design, typically, a designer is expected to provide visual mockups and a front-end developer is expected to convert the mockups into working HTML/CSS/JS code. Rarely do people design directly in the browser. In fact, my experience says that most designers consider it to be infeasible and many clients find it surprising.
However I think designing directly in the web browser makes sense.
Video: https://hasgeek.tv/metarefresh/2012/141-designing-in-the-browser