how to center main menu below header 2.0RC1?

[timned88]

i would like to center the main menu buttons below the header section in 2.0RC1.
in 1.1.x, i believe that i just used a <center> tag in index.template.php but that doesn't seem possible in 2.0RC1.

i found a way to center it (sort of) in index.css:
#main_menu
{
margin-left: auto;
margin-right: auto;
width: 50em;
}

but the problem is that the width: 50em; is a subject trial/error adjustment and i want to avoid that.
any ideas?

[greyknight17]

How about something like:

Koodi [Valitse] Laajenna

#main_menu
{
margin-left: auto;
margin-right: auto;
width: 50%;
}