如何在bootstrap中div的中间水平对齐表单

演示http://bootply.com/103569

可以使用像这样的偏移:

<div class="container">
<div class="row clearfix">
    <div class="col-md-6 col-md-offset-3 column">
        <form role="form">
            <div class="form-group">
                 <label for="exampleInputEmail1">Email address</label><input type="email" class="form-control" id="exampleInputEmail1" />
            </div>
            <div class="form-group">
                 <label for="exampleInputPassword1">Password</label><input type="password" class="form-control" id="exampleInputPassword1" />
            </div>
            <div class="form-group">
                 <label for="exampleInputFile">File input</label><input type="file" id="exampleInputFile" />
                <p class="help-block">
                    Example block-level help text here.
                </p>
            </div>
            <div class="checkbox">
                 <label><input type="checkbox" /> Check me out</label>
            </div> <button type="submit" class="btn btn-default">Submit</button>
        </form>
    </div>
</div>
<div class="row clearfix">
    <div class="col-md-12 column">
    </div>
</div>
</div>

要么

<div class="container">
<div class="row clearfix">
    <div class="col-md-12 column">
    <div class="col-md-6 col-md-offset-3 column">
        <form role="form">
            <div class="form-group">
                 <label for="exampleInputEmail1">Email address</label><input type="email" class="form-control" id="exampleInputEmail1" />
            </div>
            <div class="form-group">
                 <label for="exampleInputPassword1">Password</label><input type="password" class="form-control" id="exampleInputPassword1" />
            </div>
            <div class="form-group">
                 <label for="exampleInputFile">File input</label><input type="file" id="exampleInputFile" />
                <p class="help-block">
                    Example block-level help text here.
                </p>
            </div>
            <div class="checkbox">
                 <label><input type="checkbox" /> Check me out</label>
            </div> <button type="submit" class="btn btn-default">Submit</button>
        </form>
    </div>
    </div>
</div>
</div>

http://getbootstrap.com/css/#grid-offsetting