custom-admin-logo.php

<?php
//-> Do NOT include the opening php tag

// Custom admin dashboard header logo
add_action('admin_head', 'rvam_custom_admin_logo');
function rvam_custom_admin_logo() {
    echo '<style type="text/css">#icon-index { background-image: url('.get_stylesheet_directory_uri().'/images/logo-dashboard.png) !important; background-position: 0 0;}</style>';
}