The first challenge presents a simple page. The page requests a PNG image as its background, but if you look, the response indicates
Content-Type: text/html; charset=utf-8
Using cURL is an easy way to look at the content:
$ curl http://35.190.148.65:5001/<instance hash>/background.png
^FLAG^a3414e3ce7f841cee285f30b21cf500d422c9364ebec3b2182ef50e288bc19ec$FLAG$
Success!