Creating a webserver on a Wemos D1 mini pro
you should go for the "Advanced Webserver" example provided by the ESP8266 libraries in your Arduino IDE.
The webserver is using callbacks like

server.on ( "/", handleRoot );
server.on ( "/test.svg", drawGraph );


and so on. 
Then you can use these handles to give back a html page to your browser like

server.send(200, "text/plain", message);       //Response to the HTTP request


Note how the function returns an 200 http code to your browser, which is mandatory for showing up your web page!