Create sticky action buttons for table in Settings/User App #38215

Html structure of the table has been changed for a11y purposes: #36921.
During testing of new implementation some bugs regarding position: sticky and not right existing implementation of z-index of the action buttons have popped up. Demo:

There were 2 main problems:

1. During opening action menu of each row
2. During opening action menu of each row in editing mode

For the time reasons was decided to keep good / not broken state but without position: sticky which causes possible right scrolling inside of a table (from a11y perspective absolutely valid but not as user friendly as before), see #37870.

This is a follow-up ticket to correct action buttons to sticky position with current table implementation. There were some suggestions regarding implementation:

Current style was a bit incorrect:

• .userActions had z-index: 10
• .popovermenu had z-index: 110
• .userActions is a parent of .popovermenu
• A child cannot have z-index higher than parent

For position: relative we could just remove z-index: 10. But with position: sticky it works different... position: sticky always creates a new stacking context. It is possible neither to remove z-index from sticky parent, nor to make child with higher z-index...

If I'm not wrong, the only way to keep sticky here is to use another container for NcActions here. For example, #app-content. But > I am really not sure, it positions element correct with sticky...

For an experiment, try to set container prop of NcActions here to #app-content.

from #37860 (comment)

And:

Proposals regarding sticky + z-index issue:

Render NcActions outside the table row

• Props:
• I'd expect it to be easy to implement
• Cons:
• Requires rewriting of some integration tests because row buttons will be outside of the row

Generate progressive z-index - set each next row less z-index value

• Props:
• Keep the current structure
• Cons:
• More complex implementation
• Not sure about performance and large tables

from #37870 (comment)

Please pay attention that integration tests possibly have to be adopted too.