position() with margin: auto

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HTML

<div id="box">
    <div id="boat">Box with margin: 0 auto</div>
</div>

CSS

#box {
    position: relative;
    width: 300px;
    border: 2px solid green;
}

#boat {
    width: 100px;
    margin: 0 auto;
    border: 1px solid red;
}

JavaScript

console.log("position left:", $("#boat").position().left);
console.log("margin left:", $("#boat").css("margin-left"));