值为<code>.btn-lg</code>, <code>.btn-sm</code>, or <code>.btn-xs</code>来修改按钮的大小
                    </p>
                    <h3 class="font-bold">按钮尺寸</h3>
                    <p>
                        <button type="button" class="btn btn-primary btn-lg">大按钮</button>
                        <button type="button" class="btn btn-default btn-lg">大按钮</button>
                        <br/>
                        <button type="button" class="btn btn-primary">默认