next.js/examples/cms-sanity/next.config.ts

import type { NextConfig } from "next";

const nextConfig: NextConfig = {
  env: {
    // Matches the behavior of `sanity dev` which sets styled-components to use the fastest way of inserting CSS rules in both dev and production. It's default behavior is to disable it in dev mode.
    SC_DISABLE_SPEEDY: "false",
  },
};

export default nextConfig;