我正在WordPress中使用bootstrap。页眉在WordPress中未显示全宽。但当我在没有WordPress的情况下测试代码时，它会显示全宽的背景图像。原因是什么？

//my html

            <div class="container">
            <div class="row">
                <div class="col-xs-12">
                    <div class="header-container text-center background-image" style="background-image: url(<?php header_image(); ?>);">

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

//css settings
.header-container{
        display: block;
        position: relative;
        height: 326px;
    }
    .background-image{
        background-size: cover;
        background-position:  center center;
        background-repeat: no-repeat;
    }