HTML背景不会一直下​​降到DIV

Question

有人知道为什么我的背景图像没有一直下降吗？

这是我本节的代码，我很困惑。

        <!-- Page wrapper  -->
    <div class="page-wrapper" style="padding-bottom:0px; background-image:url('https://i.imgur.com/iLPF8lw.jpg');background-repeat: no-repeat;background-size: 100% 100%;">
        <!-- Bread crumb -->
        <div class="row page-titles" style="margin-bottom:0px !important">
            <div class="col-md-5 align-self-center">
                <h3 class="text-primary">Course Work</h3> </div>
            <div class="col-md-7 align-self-center">
                <ol class="breadcrumb">
                    <li class="breadcrumb-item"><a href="javascript:void(0)">Home</a></li>
                    <li class="breadcrumb-item active">Course Work</li>
                </ol>
            </div>
        </div>
        <!-- End Bread crumb -->    

下面是中心对象的代码

            

            <?php echo $istrial ?><br><br>
            <span style="font-weight: 600; color: black"><?php echo $course_text ?></span>
            <div class="progress interface-progress">
                <div class="progress-bar" role="progressbar" aria-valuenow="70" aria-valuemin="0" aria-valuemax="100" style="width:<?php echo $percent ?>%"></div>
            </div>
            <p style="color: red"><?php echo $percent ?>% Progress</p>
        </div>
        <hr>
        <div class="course-content" style="margin: 30px; text-align: center;" >
            <a href="course-work-proc.php" class="btn btn-primary">Resume Course</a>
        </div>
         <div style="margin: 30px; text-align: center;" >
             <img alt="Drive Along iPhone app" src="https://i.imgur.com/wBAn7J7.png"></a>
             <img alt="Drive along google play" src="https://i.imgur.com/EndFPjb.png"></a>
         </div>
    </div>    

    <!-- footer -->
    <!--<footer class="footer" style="margin-top:0px; margin-bottom: 0px"> © 2018 All rights reserved.</footer>-->
    <!-- End footer -->
</div>
<!-- End Page wrapper  -->