I want to set transparent header on every page of my website and keep at the same time the breadcrumb section under the header when I scroll down the page.
At the moment, when you’re at the top of the page, the breadcrumbs section is at the top of the page under the transparent header : I’d like to have transparent breadcrum section under the header/main nag section. And when you scroll down the header/main nav becomes white, which is fine, but the breadcrumbs disappear which is something I do not want. Can you help ? Thanks a lot

I see, not sure I understand why you want the transparent header if you are to have nothing below it, but you can push down the page content with the size of the header so that the Heading section (the one that holds the breadcrumbs) shows below it, for example try this:

.page_title_bgr .full_container_page_title {
    margin-top: 140px;
}

Where the value of margin top would be the height of your header. You can do this globally in Theme options -> Custom CSS, or on a per page basis under Page settings (the cog icon in the editor).

Not really clear… If you have an image below the transparent header your breadcrumb area if you have it switched on will appear above that ROW that holds the image. And it would be somewhere behind the transparent area – not really a cool effect.
And how exactly would you want the “breadcrumbs to be transparent as well”??
I think it would be best if you describe what you are after in a screenshot… only then I could possibly realize it and see if I can help

You have to customize and rework the current functionality then, as it’s not even similar to what you are after.
Basically you need to override your “boc_page_header” method found in the \fortuna\includes\boc_framework.php. You can do that in your child theme. Your custom CSS would go there too. Have in mind that this is quite a customization you are after I hope you have the coding skills to achieve it. Good luck!