css center problem

<div id="headermain">
 <div id="logo">
            <a href="#">net</a>
        </div>

i'm unable to center the #logo div inside of #headermain

i'm giving margin:auto; but nothing happends. #he开发者_开发技巧adermain is also centered by using margin:auto;

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Use width property :

 #headermain { width: 1000px; margin: 0 auto; }
 #logo { width: 400px; margin: 0 auto; }

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div#logo must have a width property for margin: auto; to work

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Is it? #logo { text-align: center }