the class .btn can be use to create a simple button, you can change the color of a button by using btn-{theme/color}
<button class="btn">
Default
</button>
<button class="btn btn-primary">
Primary
</button>
<button class="btn btn-primary-outline">
Primary Outline
</button>
<button class="btn btn-primary-flat"x>
Flat
</button>
<button clas="btn btn-icon">
<span class="material-icons">add</span>
<button>
there are 6 buttons size from 1 (smallest) to 6 (biggest), been size-2 the default size for button
<button class="btn btn-size-1">
btn-size-1
</button>
</button class="btn btn-size-2">
btn-size-2
</button>
</button class="btn btn-size-4">
btn-size-3
</button>
you can create button groups by using a div with class .btn-group
<div class="btn-group">
<a class="btn">1</a>
<a class="btn">2</a>
<a class="btn">3</a>
</div>