CSS only working when I'm logged in

I’m really new to this, the last time I made a website I was using Greymatter and MS Frontpage and iframes, so I spent all day yesterday reading about WordPress and I managed to get a fairly basic theme working for my website (datemyfriendtina.com). I made it live and then realized that while i was logged-in to WordPress everything was perfect but when I logged out all the font formatting was gone. It’s not that the whole style sheet doesn’t work because the background and div colors are still there.

Logged In: http://imgur.com/5N5qmRI
Logged Out: http://imgur.com/ZtHFWRU

I searched before I posted this and it seems that i’m not the first person to have this issue but most were permissions issue, I don’t think that my problem. I also don’t have that WP Cache plugin enabled.

I found one person who said they had figured out that the class name changed when they were logged in and solved the problem but the didn’t elaborate and it was over a year old and closed. I feel like my problem is along those lines but I’m not strong enough with the code to figure it out.

Thanks in advance.

Bonus question: is there a way to center the header and content div layers?