admin_navigation.php

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
<style>
    .side-nav{
        top:61px;
    }
</style>
<nav style="background-color:#3a223a;" class="navbar navbar-inverse navbar-fixed-top" role="navigation">
            <!-- Brand and toggle get grouped for better mobile display -->
            <div class="navbar-header">
                <button type="button" class="navbar-toggle" data-toggle="collapse" data-target=".navbar-ex1-collapse">
                    <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="index.php"><img style="width: 140px;height: 35px;position: relative;bottom: 5px;" src="header_img2.png" /></a>
            </div>
            <!-- Top Menu Items -->
            <ul style="top: 61px;" class="nav navbar-right top-nav">

                  <li><a href="">Users Online: <?php echo users_online(); ?></a></li>

               <li><a href="../index3.php">Blog Page</a></li>

                <li class="dropdown">
                    <a href="#" class="dropdown-toggle" data-toggle="dropdown"><img style="width: 30px;height: 30px; cursor:pointer;" src="user.png"/>
                    <?php

                    if(isset($_SESSION['username'])){
                        echo $_SESSION['username'];
                    }

                    ?>
                    </a>
                    <ul class="dropdown-menu">
                        <li><a href="../profile.php" >Profile</a></li>
                        <li><a href="#">Settings</a></li>
                        <li class="nav-divider"></li>
                        <li><a href="../includes/logout.php">Logout</a></li>
                    </ul>
                </li>
            </ul>
            <!-- Sidebar Menu Items - These collapse to the responsive navigation menu on small screens -->
            <div class="collapse navbar-collapse navbar-ex1-collapse">
                <ul class="nav navbar-nav side-nav">
                    <li>
                        <a href="index.php"><i class="fa fa-fw fa-dashboard"></i> Dashboard</a>
                    </li>

                    <li>
                        <a href="javascript:;" data-toggle="collapse" data-target="#posts_dropdown"><i class="fa fa-fw fa-arrows-v"></i> Posts <i class="fa fa-fw fa-caret-down"></i></a>
                        <ul id="posts_dropdown" class="collapse">
                            <li>
                                <a href="posts.php">View All Posts</a>
                            </li>
                            <li>
                                <a href="posts.php?source=add_post">Add Posts</a>
                            </li>
                        </ul>
                    </li>
                    <li>
                        <a href="categories.php"><i class="fa fa-fw fa-wrench"></i> Categories</a>
                    </li>

                    <li >
                        <a href="comments.php"><i class="fa fa-fw fa-file"></i> Comments</a>
                    </li>
                   <li>
                        <a href="javascript:;" data-toggle="collapse" data-target="#demo"><i class="fa fa-fw fa-arrows-v"></i> Users <i class="fa fa-fw fa-caret-down"></i></a>
                        <ul id="demo" class="collapse">
                            <li>
                                <a href="users.php">View All Users</a>
                            </li>
                            <li>
                                <a href="users.php?source=add_user">Add New User</a>
                            </li>
                        </ul>
                    </li>
                    <li>
                        <a href="profile.php"><i class="fa fa-fw fa-dashboard"></i> Profile</a>
                    </li>
                </ul>
            </div>
            <!-- /.navbar-collapse -->
        </nav>