@advanced-rest-client/arc-overlay-mixin/arc-overlay-backdrop.d.ts

arc-overlay-mixin is a port of iron-overlay-behavior that works with web components

import { ArcOverlayBackdrop } from './src/ArcOverlayBackdrop';

declare global {
  interface HTMLElementTagNameMap {
    "arc-overlay-backdrop": ArcOverlayBackdrop;
  }
}