hardcoded url and missing main.css

[davtur19]

https://github.com/vlang/vorum/blob/c1256574bfdb828824f0e194151b8975b650be6c/header.html#L7 https://github.com/vlang/vorum/blob/c1256574bfdb828824f0e194151b8975b650be6c/header.html#L12