I would like to build a browser based persistent online strategy game. Something in the vein of Evony, nothing requiring a particularly complex UI. I'm a reasonably skilled backend software engineer and hate fiddling around with html/css to try and make UI elements look/behave right instead of working on game design / logic. I've messed around with Unity as well, but 90% of my time still ends up mucking about with the UI.

Assuming I have a webserver with all the communication endpoints it needs already built, are there any good simple 2d oriented game engines for building out a browser-run game? If there isn't really an “engine" with game loops and all, is there a good website design tool that people have used for making games that is mostly drag/drop with UI/JS interactions and exports all the html/js/css files needed?

I don't think you're going to have much luck finding tools to help you there. /Someone/ is going to have to do the work to create the UI, and it'll have to be either you or someone you hire or partner with.

Since it's browser based, you could build it in (for example) React, and structure it so you have separate logic and presentation components - then you are free to implement the whole frontend without caring too much about presentation, and the presentation can be worked on in parallel by someone else or fixed later. I guess in principle there could be a library of such gaming-UI React components that would act as an ideal starting-point to extend and customize, but I've never come across any.

Alternatively, have you looked at HTML5-based engines, like Phaser or Playcanvas? Not that they're going to give you a significantly more streamlined webgame-experience than Unity or Godot.

I've trying something similar now, and I agree with Brian Sandberg.

My advice is to find a javascript framework (React, Vue, Svelte) that clicks with you, and learn it properly. You're going to have to do a whole bunch of “mucking about with the UI” regardless, but from my experience so far (with Svelte) I'd much rather do this with Svelte, JS, CSS, HTML then with UI components in Unity / Godot / Unreal etc.

Not only is it a relatively clean way of coding a UI, it's also a marketable skill. I'm trying to make a procedural persistent RPG, and the front-end process is actually getting to be quite fun. It's a different kind of puzzle solving compared to backend dev, and I much prefer it over 3D game engine UI systems.