Add filters to widgets and rows stylesheet

Hi,
I want to be able to change the margin bottom of a particular widget.
to do so, like the widget padding, I thought it would be a good idea to add margin bottom under layout.
I managed to add the setting – but apparently, I don’t have a filter to use with the margin bottom for the widget.
File: siteorigin-panels.php
Function: siteorigin_panels_generate_css

// Add the bottom margins

$css->add_cell_css($post_id, false, false, '.so-panel', array(

    'margin-bottom' => $panels_margin_bottom.'px'

));

$css->add_cell_css($post_id, false, false, '.so-panel:last-child', array(

    'margin-bottom' => 0

));

// Filter the bottom margin for this row with the arguments

$css->add_row_css($post_id, $gi, '', array(

    'margin-bottom' => apply_filters('siteorigin_panels_css_row_margin_bottom', $panels_margin_bottom.'px', $grid, $gi, $panels_data, $post_id)

));