New to html, need someone to help me understand why I can't get my code to work

Hey so I just learned abt semantic html and i edited this web game im working on and would like some help getting it back to working order. i wanted to get the uppermost line of text on the page to have white text and a cornflowerblue background, center the form vertically and horizontally, put space inbetween the username and password entry and submit button vertically, and put a border around each of the three uppermost lines of text.

pictures in google doc


this is what it currently shows