Login form in header question

I’m trying to add a small login form in my header. I want the “username” “password” text to appear inside the box forms, without any buttons (just press enter) and the login form replaces with something like “welcome USERNAME, visit your dashboard, logout” after they log in. Similar to what this site uses.

I’ve searched google and the forums for an example code, but they are all missing something. Does anyone know of such a code example I could use? I can style it myself, I just don’t understand how to add the text inside the boxes to save space, and have it work without an actual login button.

Any help is appreciated, thanks.