Hacker One CTF - A little something to get you started
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^{redacted}$FLAG$
Success!