Describe the bug
The button called "toolbar-handler", locate inside the toolbar, have a fixed aria-label="Shrink toolbar" even having an expand/shrink behavior and don't have enough contrast.

• fix the aria-label to work with both status (expand and shrink)
• Correct the contrast for the toolbar handler button

To Reproduce
Steps to reproduce the behavior:

1. Go, using a screen reader and shift + tab keys, to the button that controls the toolbar
2. Press enter, the toolbar will shrink
3. Another press, the toolbar will expand.

Expected behavior
The screen-reader needs to know when the toolbar is open/closed and must have a properly aria-label (or something related) for each behavior and read it each time.

Increase the button bar contrast

Screenshots

Software (please complete the following information):

• Volto Version 17.0.0-alpha.19
• Plone Version 6.0.4

Additional context
There is some question to answer about this button:
This button needs to be accessible by a screen-reader?
Why a user using a screen reader need to shrink/expand this toolbar?