If you're coming from the WPF and winforms world IMHO you actually should find and use a framework. Find something that has a bunch of pre built components like

If you're coming from the WPF and winforms world IMHO you actually should find and use a framework. Find something that has a bunch of pre built components like cards, dialogs, buttons, etc. already styled and ready to go. You could go for something complex like react and a component library in its world, or go with something that is (mostly) CSS like bootstrap or bulma. I say this because where you're coming from you're used to plopping down a dialog and throwing components like forms and buttons and such on it. With plain HTML and CSS it is much, much more free form and you can easily be paralyzed by choice or indecision with how to design or even just how to layout components. With a framework like bootstrap you're given layout primitives like a grid and higher level components like a navigation bar, menus, etc. which are much closer to what you're used to from C# and windows.