LitElement not working in TypeScript project

🐛 bug report

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Description of the problem

I'm not able to create a TypeScript project that can use the next versions of LitElement and lit-html.

I'm starting with a vanilla TypeScript project and then adding a dependency on lit@2.0.0-pre.1. On importing this into index.ts:

import { LitElement, html } from "lit";
import { customElement } from "lit/decorators.js";

@customElement("my-element")
export class MyElement extends LitElement {
  render() {
    return html`<h1>Hello</h1>`;
  }
}

I get source errors that TypeScript can't find the module 'lit'.

Then in the preview window I see errors that I "Cannot use import statement outside a module" as in https://github.com/codesandbox/codesandbox-client/issues/5464

Next, I tried to remove Parcel from the equation to get to a more vanilla project, thinking that Parcel can't handle the ES2020 in the lit package. I edit package.json:

  "scripts": {
    "start": "web-dev-server --node-resolve",
    "build": "tsc"
  },
  "dependencies": {
    "lit": "2.0.0-pre.1"
  },
  "devDependencies": {
    "@web/dev-server": "^0.1.8",
    "typescript": "^4.2.0-beta"
  },

and modify index.html to import the compiled module directly with:

    <script src="lib/index.js" type="module"></script>

This should set up a very vanilla TypeScript project that serves individual compiled modules. The error is now "Could not find module in path: './lib/index.js' relative to '/index.html'"

How has this issue affected you? What are you trying to accomplish?

Trying to use Lit's preview release.

To Reproduce

Link to sandbox: link (optional)

Your Environment

Start with the linked sandbox and compare its index.ts, package.json, and index.html against the reported TypeScript and web-dev-server setup. Reproduce the TypeScript module-resolution and preview errors, then trace how the project handles Parcel, tsc output, and module imports. Done means a vanilla TypeScript project can import lit and run its preview without these errors.