有没有办法在我的html div上获取响应式背景图片

Question

我遇到问题，无法正确解决。有带有注册表格的标头，但我无法响应背景图片。我已经阅读了很多手册，但是没有用。

   .background-img {
			background-image:url('http://lorempixel.com/1920/655/');
			-webkit-background-size: cover;
			-moz-background-size: cover;
			-o-background-size: cover;
			background-size: cover;
			background-repeat: no-repeat;
			width: 100%;
			height: auto;
		}

             <div class="landing background-img">
             <div class="overlay">
                <div class="container">
                    <div class="row">
                        <div class="col-md-7">
                            <!-- /.main title -->
                            <h1 class="wow fadeInLeft text-center">
                                Header phrase
                            </h1>
                        </div>
                        <!-- /.signup form -->
                        <div id="reg">
                            <div class="col-md-5 ">
                                <div class="signup-header wow fadeInUp">
                                    <h2 class="form-title text-center"     id="signup_title">Register</h2>
                                    <form class="form-header" role="form"     method="POST" id="#">
                                        <div class="form-group" id="mask">
                                            <input class="form-control input-lg" name="username" id="phone_reg" type="text" placeholder="Phone" required>
                                        </div>
                                        <div class="form-group">
                                            <input class="form-control input-lg" name="password" id="password" type="password" placeholder="Pass" required>
                                        </div>
                                        <div class="form-group last" id="reg_block">
                                            <input class="btn btn-warning btn-block btn-lg" id='popup_login_in_pass' onclick="getPassForPhone()" value="GetPass">
                                            <input type="checkbox" id="is_send_sms" onclick="showIsSMSEnter(this)">&nbsp;<span id="is_send_sms_label">SMS is here</span>
                                        </div>
                                        <div class="form-group last">
                                            <input type="submit" class="btn btn-warning btn-block btn-lg" id='enter' value="Enter">
                                        </div>
                                        <p class="error_reg_result text-center">some text</p>
                                        <small class="time_reg_result" style="display: none">SMS will come after <span class="time_reg_sms">60</span> sec.</small><br>
                                    </form>
                                </div>
                            </div>
                        </div>
                    </div>
                </div>
            </div>
        </div>

如果我更改背景尺寸：达到背景大小：图像变得敏感，但是即使我将其设置为高度，它也会改变高度：100％;

我如何实现我的目标？