bootstrap 3 arrow on dropdown menu

You need to add :after and :before css rules to your dropdown-menu. These rules are taken from Bootstrap 2, and are what draw the triangle above the dropdown.

JSFiddle DEMO

.dropdown-menu:before {
  position: absolute;
  top: -7px;
  left: 9px;
  display: inline-block;
  border-right: 7px solid transparent;
  border-bottom: 7px solid #ccc;
  border-left: 7px solid transparent;
  border-bottom-color: rgba(0, 0, 0, 0.2);
  content: '';
}

.dropdown-menu:after {
  position: absolute;
  top: -6px;
  left: 10px;
  display: inline-block;
  border-right: 6px solid transparent;
  border-bottom: 6px solid #ffffff;
  border-left: 6px solid transparent;
  content: '';
}

Confused how? See here for an animation that explains css triangles