My ESP8266 web server is only displaying text, even after ensuring content type is text/HTML So I just got my two ESP8266/ESP-12E WiFi development boards in the mail as I am trying to set up a few home automation devices in my house. I've gotten much further than I thought I would today, considering this is my first foray into working with circuits that involve microprocessors/WiFi, but I've run into a problem that I can't find a solution to myself.  Forgive me if there is another question similar to this, but I could not find it and this seems like the best place to ask.

I am using a tutorial/template program that Rui Santos from Random Nerd Tutorials was kind enough to create ( https://randomnerdtutorials.com/esp8266-web-server/ ), and although we have (as far as I can tell) identical boards, operating systems and Arduino code, I keep getting an HTML page that is text only, with none of the CSS or HTML elements showing.  It should look like this:



However, I am getting a page that looks like this:



His serial monitor is giving this response:



My serial monitor is giving me this response:



I've tried putting client.println("Content-type:text/html"); in a few places to see if it would help display the page, but to no avail.  Any help with getting this little program/website running would be greatly appreciated. 

Thanks for your time!
Don't use the low-level tools to handle http, use the built-in http tools. They  make creating http responses trivial. No more concatenating headers or worrying about client status; it provides a nice clean function ex:server.send(404, "text/plain", message); and nice subscription method: server.on().

Checkout its usage on one of the Arduino ESP8266's built-in examples:
https://github.com/esp8266/ESPWebServer/blob/master/examples/HelloServer/HelloServer.ino