Both.
The Delphi, C++ Builder, Forms/WPF/UWP, Swing/JavaFX soul in me begs to differ.
In fact that is the biggest pain in Web projects to this day and I can hardly wait for stuff like Uno and Blazor to bring "Flash" back, if Web Components don't do it first.
You really don't want to add ephemeral designer tools to your list of hard project dependencies.