不以页边为中心的Div / Text:auto

I am trying to use a @media query, everything is working fine, except id like to have text become centered with margin:auto when the @media query is called. I have tried soooo many things. I originally had float:left in #masterhead #header-text{} but I have changed that to display:inline-block; (I have read that, that was a solution for many). I have tried explicitly setting widths.. and display:block;I am trying to use a @media query, everything i