add_action( 'admin_head', 'wpso_add_admin_custom_css' );

function wpso_add_admin_custom_css() {
    // Bail if Admin.
    if ( current_user_can( 'manage_options' ) ) {
        return;
    }
    ?>
    <style>
        body {background-color: #DED51F; }
    </style>
    <?php
}