Rounded
The "rounded" family really is part of be-bdr, however, to make class names as short as possible the "bdr" has been omitted. So instead of having be-bdr-rounded-top, the result has been be-rounded-top.
<button class="be-btn be-btn-ghost be-rounded-left be-hover-clouds"><<</button>
<button class="be-btn be-btn-ghost be-rounded-right be-hover-clouds">>></button>
.be-rounded
.be-rounded-top
.be-rounded-bottom
.be-rounded-left
.be-rounde-right
.be-circle
.be-bdr-pill