<button class="btn btn-blue">Blue</button>
		<button class="btn btn-green">Green</button>
		<button class="btn btn-yellow">Yellow</button>

		<button class="btn btn-blue-outline">Blue</button>
		<button class="btn btn-green-outline">Green</button>
		<button class="btn btn-yellow-outline">Yellow</button>

Note: To use bootstrap v4 tooltip option you need to load tether.js.

Important [trick]: What bootstrap developers not explained today I release this note istether.js must be load after JQuery.js and before bootstrap.js.