Adding styled-components theme auto-completion

styled-component.d.ts

import { ThemeType } from "./theme";
import "styled-components";

declare module "styled-components" {
  export interface DefaultTheme extends ThemeType {}
}

theme.ts

export const theme = {
  fonts: ["..."],
  sizes: [6, 12, 16, 20]
}

export type ThemeType = typeof theme;