Twitter Bootstrap - why row class has margin-left: -20px?

Question

I don't understand why row class has margin-left: -20px (so it grows after parents border like on the image). I think nobody needs this behavior. Or am I doing something wrong?

<div class="container">
        <div id="top-container" class="row">
            <div class="span8">
                <h1>App</h1>
            </div>
            <div class="span4">

            </div>
        </div>
    </div>

Answer 1

You can use row-fluid instead of row, then your span4 and span8 won't have margin-left.

<div class="container">
    <div id="top-container" class="row-fluid">
        <div class="span8">
            <h1>App</h1>
        </div>
        <div class="span4">

        </div>
    </div>
</div>