How to remove Help tab and the Dashboard widget area’s empty border

The code below will remove the Help Tab and will hide the extra two Dashboard widget areas:

add_action( 'admin_head', 'wpse209151_dashboard_cleanup' );
function wpse209151_dashboard_cleanup() {
    $screen = get_current_screen();

    // Bail if we're not looking at the dashboard
    if ( 'dashboard' !== $screen->base ) {
    return;
    }

    // Deal with the Help Tabs
    $screen->remove_help_tabs();

    // Hide the desired Dashboard widget areas 
    // 4 available widget areas: #postbox-container-1,2,3,4
    echo '<style>
        #postbox-container-3,
        #postbox-container-4 {
            display: none;
        }
    </style>' . "\n\n";
}