@Sub 6 Resources already answered this question wholly but I want to add a bonus tip. If you already added implementation 'com.android.support:design:27.1.1' to your code and the compiler can't still resolve the FloatingActionButton class, simply rebuild your project. A colleague and I recently had this same problem while the dependency was already there and a simple rebuild solved it all.

I hope this helps.. Merry coding!

@Sub 6 Resources already answered this question wholly but I want to add a bonus tip. If you already added implementation 'com.android.support:design:27.1.1' to your code and the compiler can't still resolve the FloatingActionButton class, simply rebuild your project. A colleague and I recently had this same problem while the dependency was already there and a simple rebuild solved it all.