middleware.ts

import { NextRequest, NextResponse } from "next/server";

export default async function middleware(request: NextRequest) {
  if (request.headers.get("Accept")?.includes("text/html")) {
    const response = NextResponse.next();
    response.headers.set(
      "Accept-CH",
      `Sec-CH-Prefers-Color-Scheme, Sec-CH-Prefers-Contrast`
    );
    response.headers.set("Vary", "Sec-CH-Prefers-Color-Scheme");
    response.headers.set("Critical-CH", "Sec-CH-Prefers-Color-Scheme");
    return response;
  }
  return NextResponse.next();
}