如何在导航栏上覆盖图像？

我只想简单地使图像也覆盖导航栏，但是我对现在该如何做感到非常困惑。

图片

目前，导航栏和图像是分开的，如果可能的话，我也希望导航栏的背景也是图像

HTML代码

<!-- Navigation -->
    <nav class="navbar navbar-inverse navbar-fixed-top" role="navigation">
        <div class="container">
            <!-- Brand and toggle get grouped for better mobile display -->
            <div class="navbar-header">
                <button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1">
                    <span class="sr-only">Toggle navigation</span>
                    <span class="icon-bar"></span>
                    <span class="icon-bar"></span>
                    <span class="icon-bar"></span>
                </button>
                <a class="navbar-brand" href="#">Start Bootstrap</a>
            </div>
            <!-- Collect the nav links, forms, and other content for toggling -->
            <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
                <ul class="nav navbar-nav">
                    <li>
                        <a href="#about">About</a>
                    </li>
                    <li>
                        <a href="#services">Services</a>
                    </li>
                    <li>
                        <a href="#contact">Contact</a>
                    </li>
                </ul>
            </div>
            <!-- /.navbar-collapse -->
        </div>
        <!-- /.container -->
    </nav>

    <!-- Full Width Image Header -->
    <header class="header-image">
        <div class="headline">
            <div class="container">
                <h1>join our movement!</h1>
                <!-- <h3>Join Now</h3> -->
                <button class="btn btn-success btn-lg">Join Now</button>
                <!-- <button type="button" class="btn btn-primary btn-md">Medium</button> -->
            </div>
        </div>
    </header>

CSS代码

.header-image {
    display: block;
    width: 100%;
    height: auto;
    text-align: center;
    background-image: url("/images/cloud6.jpg");
    -webkit-background-size: cover;
    -moz-background-size: cover;
    background-size: cover;
    -o-background-size: cover;
}