Centering an image / Float

Hello, sorry to bother you with a silly question. I’ve starting working with programming and WordPress from just a couple of weeks.

My problem today is that I have a log shifted to the left and I would like to have it centered. Unfortunately float doesn’t have this option.

The code is;

/* 2.3 Header */
#header{padding:30px 0 30px;clear:both;position:relative;}

#logo  { float: left; }
#logo img  { }
#logo .site-title, #logo .site-description  { color: #000; display:none;  }
#logo .site-title a { color:#222; font-size:40px; line-height:40px; text-transform:none; font-weight:bold; text-decoration:none; }
#logo .site-title a:hover { text-decoration:underline; }
#logo .site-description { color:#999; }

Any idea what could I use for centering the logo (without giving the size of the logo itself?). I already tried with “margin-left: auto; margin-right: auto;” but unfortunately it doesn’t work. 🙂