Coloring page wrapper

Been trying to set up colors for dw3css custom theme. On the theme settings page for my subtheme (which I have installed as default), setting a color (e.g., w3-yellow) for the Page Wrapper Background color does not seem to have any effect. After mucking around with Firefox developer and style editor I was able to make a change by changing:

.w3-theme-l5 {
  color: #000 !important;
  background-color: #140202 !important;
}

inserting the #140202 as the color in w3-theme-custom.css in the d8w3css/css/w3-css-theme-custom directory.

The theme appearance set up page seems to imply that you can change this color right from the input field by inputting "w3-yellow" (or another color.

I'm wondering if this could be because the page wrapper is not listed as a region in the info.yml file? Looking at the w3css_theme.theme that appears to do the set up we have:

  $form['drupal8_w3css_theme_settings']['w3_colors']['color_page_wrapper'] = [
    '#type' => 'textfield',
    '#title' => t('Enter Page Wrapper Background color, Text Color or any W3.CSS classes'),
    '#default_value' => theme_get_setting('color_page_wrapper'),
  ]

but there is no region named "page_wrapper", For most of the regions where the color setting appears to work properly there seems to be a corresponding region for the in the info_yml file.

Sorry if I am off base on this. If so, perhaps a simple explanation of how to change the page_wrapper would suffice.