The close button for floating badges is available in all the Reviews apps! 
You can enable it on Layout tab → Customize → Show Close Button:
What else?
There are some additions tagging along with the close button:
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When closed, the widget will pop up again in 24 hours.
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Color for the ‘cross’ can be set in Appearance tab → Badge → Close Button Color
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If Sources and Title are disabled, the close button displays a bit lower:
We’ll be happy to hear your feedback on this update, so feel free to share! 