Simple centering of block

[linuxdream]

Sorry for the dumb question but I normally don't do CSS much. If you have div block and apply two classes to it, one containing a width and the other containing auto left and right margins, why won't it center the block?

 

.width150{
    width: 150px;
}

.blockCenter{
    margin-left: auto;
    margin-right: auto;
}

<div class="width150 blockCenter">
    content here
</div>

 

It centers the block fine when I put the width and margins in one CSS class. But shouldn't it work fine separated like the above code since the width should be seen for the margins to center properly? Any help is appreciated. 

[ifubad]

it's centering fine as is with FF2, IE6 7 & 8. What browser r u using?

 

also, no need to use two separate declarations for the margin, just use

 

margin: auto; /*covers both left and right*/

[linuxdream]

Ahh, thanks for the consolidation tip. I'm on FF 3.0.11 on Mac. Yea, I would think I should work fine, I'll have to debug more and see what else may be causing it. Thanks for the outside check!