Problematic border-collapse in HTML editor (border-radius does not work)

[eveneme]

Prerequisites

• I have searched for duplicate or closed issues
• I can recreate the issue with all plugins disabled

Describe the issue

Roundcube mail does not display border-radius in the added signature, but when I send an email to Gmail or Outlook, the border-radius is displayed. I would also like to add that if I have a box-shadow set, the border-radius is displayed, but when I have just a regular border and border-radius, the border-radius does not appear.

Roundcube:

Gmail:

What browser(s) are you seeing the problem on?

Chrome

What version of PHP are you using?

8.1

What version of Roundcube are you using?

1.6.9

JavaScript errors

No response

PHP errors

No response

[alecpl]

In mail preview or mail composer? We'll need the HTML code.

[eveneme]

While composing a new email message
stopka.txt

[alecpl]

TinyMCE adds table { border-collapse: collapse; } style which is the problem, I suppose. We could overwrite this style, but I'm not sure we should.

EDIT: I didn't try but this option might be useful https://www.tiny.cloud/docs/tinymce/latest/table-options/#table_default_styles