Toolset for rapid UI development for web applications?

I'm looking to build a web app, and user interfaces are the biggest problem for me. It takes a long time to build a simple interface with HTML editing approach. You need to find a CSS framework, think of the layout, encode it in code. If you're not too expert in CSS, you're going to struggle. While doable for a larger projects, I find the above approach not suitable for rapid prototyping. I'm looking for a good visual editor with a drag-and-drop to build web apps out of smaller components. The closest one I found is the Swift editor in xCode (https://developer.apple.com/docu...) - you get the flexibility of code editing while having the speed of a robust drag-n-drop app builder. For the web, I didn't find good solutions like that so far. There is a ton of "website builders" on ProductHunt, but they most frequently are intended for simple landing pages, maybe blogs - but not complicated web apps which are supposed to be backed by some logic. On the other hand there are app builders like ReTool, but they are for internal tools, don't allow much design customizability, and cost a fortune. All of those alternatives I found are "black-boxes": you don't get the HTML so you can't use seamlessly a framework like React. So I'm curious: what do you use for HTML/CSS UIs for rapid prototyping?