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// force one-column dashboard
function shapeSpace_screen_layout_columns($columns) {
    $columns['dashboard'] = 1;
    return $columns;
}
add_filter('screen_layout_columns', 'shapeSpace_screen_layout_columns');

function shapeSpace_screen_layout_dashboard() { return 1; }
add_filter('get_user_option_screen_layout_dashboard', 'shapeSpace_screen_layout_dashboard');
add_action( 'admin_head-index.php', function()
{
    ?>
    <style>
        .postbox-container {
            min-width: 100% !important;
        }
        .meta-box-sortables.ui-sortable.empty-container {
            display: none;
        }
    </style>
    <?php
});