Check if button appears next to all block elements except image (no toolbar item available).
Change format of one of the block elements, panel attached to button should hide after that.
Put selection in the one of the last blocks, click on button to display panel then start resize browser window
and observe if button and panel are properly repositioned.
External changes
Typing
Click Start external typing
Put selection to the first paragraph (Like all the great things...) and click the button to open panel (be quick).
Check if button and panel are repositioned correctly.
Removing
Click Start external deleting
Put selection to the first paragraph (Like all the great things...) and click the button to open panel (be quick).