Align background image counting pixels from the center?

I realized the only way to get a background image properly aligned was counting pixels from the center, since using % and counting pixels from the left sometimes overlays images depending the screen size.

There must be a way to align it properly.

Is ther开发者_如何学编程e a way to align the background image horizontally counting pixels from the center?

Thanks

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With CSS I would use something like this.

div.background{
    position: absolute; 
    left: 50%; 
    margin-left: -100px;
}

The margin-left would be exactly half of the width of the background.

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background-position:center top;