Centering a SPAN

programming web dev
1 

#someBox {
   margin: 0 0 0 40%;
   background: red;
}

<span id="someBox">some text</span>

I’m having difficulty centering a span (variable width) in 3 major browsers. If I add “display: block; width: 20em;”, everything is consistent with all 3 browsers, but I really didn’t want static width.

[LIST]
[]IE7: no background
[]Safari: left justified
[*]FF: perfect
[/LIST]