Export to PDF - missing frames in tables

Hello,

Contao ver 3.5.20

I create table in text inside article.
In the browser preview this table has a frame.
Unfortunately when I export this page to PDF there are no frames in tables (contents of frame is OK)

We use theme: OpenSauce and view of frame if defined in main.css from OpenSauce.

I tested also version without CSS (I commented table{...} etc in main.css) I set for table border width 1 in HTML - the result is the same - no table frames in PDF.
After that I installed module pdf-template and I tried to define table frames in tcpdf.css -the result is the same - no table frames in PDF

I see on TCPDF vendor pages that export to PDF should work correctly with table frames so, I assume it should for also in Contao.

Any suggestion how to get table frame in PDF in Contao?

Slawomir