Tables style should not rely on scope attribute

[deniak]

Describe the issue
The table component relies on the scope attribute to style the headers.

th[scope="col"] {
  background-color: #024488;
  color: #fff;
}

Removing/Forgetting that attribute will remove the blue background.

Recommended solution
Updating the selector to thead > th will make that attribute optional and ensure all the tables have the same style.

Additional request
We might also need the same changes for tables footer tfoot.

[NicolaSaunders]

This rule was originally intended in the spirit of "defensive coding", where the lack of the desired visual appearance was aimed at reminding the author of the markup to add the missing scope="col" attribute.

However, I have learned that the scope attribute is not as crucial as I had previously thought for headers in simple tables:

• https://adrianroselli.com/2023/02/avoid-spanning-table-headers.html#Verdict
• https://www.tpgi.com/short-note-on-scoping-mechanisms/

Plus, it was too restrictive to tie the style just to a column scope, when more complex tables may benefit from having the same styles for header cells with row scope. So I am happy to remove the scope attribute entirely for the th selector.

Since heading cells can exist in either thead or tfoot I don't see a need to reference either of those in the th selector.

Proposed fix is at w3c/w3c-website-templates-bundle#148