[codelabs]: Boring to Beautiful Code snippets marked up incorrectly

The following codelab:

https://codelabs.developers.google.com/codelabs/flutter-boring-to-beautiful#2

Uses a dark-to-light icon that changes the background of the code snippet section from dark to light. It should be a copy icon, which copies the code snippet to the clipboard. 

Please replace theme changing icon + action to copy icon + copy action