NGFB's Facebook Like button should not show a transparent dialog

When I click on NGFB’s Facebook Like button on any page at my site Mozaikar.cz, a dialog appears.
But the dialog is transparent and it should not be. It can discourage visitors.

To resolve it, I have:

• googled for “ngfb opacity”, “ngfb opaque”, “ngfb transparency” and “ngfb transparent” but have not found any relevant posts,
• searched for “opacity” in my site’s CSS but have not found any relevant occurrence,
• tried various settings of NGFB but have not found a resolution.

The “Add Hidden Debug Info” option on the Advanced settings page is checked.

Thanks for any suggestion that can help.

https://www.ads-software.com/plugins/nextgen-facebook/