a11y - Default sidebar "plone site" - Focus and labels - cms ui

[Wagner3UB]

Describe the bug
The default sidebar have lots of problems with accessibility, including the right use of 'focus,' lack of 'aria-label' on checkboxes and selects or the aria-labeled-by doesn't exist, and some items are missing translation.

This work must be done item by item, line by line, because there are many missing features when it comes to accessibility.

-On several elements, the focus is not visible, for example on checkboxes, but more generally in input fields, often only the insertion cursor appears.

• Checkboxes all without labels, selects with autocomplete, often not correctly associated and with no translation;

• Items visible focus

• items correct labels

• Items with a proper behavior with the current content

To Reproduce
Simple use of "tab" and a screen reader inside the sidebar

Expected behavior
Check all labels of contextual sidebars, especially for checkboxes, and associate accessible 'aria-label' to select lists with search
Make the focus visible in all fields that receive it and require interaction.

Screenshots
It's a bit challenging to demonstrate this issue because what we need to observe is precisely what we're not seeing. I attempted to record a video starting the tab sequence from the beginning of the sidebar, but the focus occasionally vanishes (for instance, inside the objectBrowser field) or is non-existent, causing confusion.

Registrazione.schermo.2023-08-24.alle.14.09.28.mov

I did not register with the screen reader on because it might be confusing, as the screen reader creates a visual border around focused items.

Software (please complete the following information):
Volto Version 17.0.0-alpha.19
Plone Version 6.0.4

Additional context
There are many others issues for the sidebar, it's impossible to create just one issue to resolve all