bootstrap 3 arrow on dropdown menu

In bootstrap 2 the dropdown menu had an upwards arrow as it can be seen here (i am not talking about the carret). Now using bootstrap 3 or latest git this arrow doesn't exist in my simple example bellow nor in the examples on the bootstrap homepage.

How can I add this arrow again using bootstrap 3?

  <li class="dropdown">
    <a href="#" class="dropdown-toggle" data-toggle="dropdown">
      Menu
      <b class="caret"></b>
    </a>
    <ul class="dropdown-menu">
      <li><a href="#">a</a></li>
      <li><a href="#">b</a></li>
      <li><a href="#">c</a></li>
    </ul>
  </li>

PS:To be precise the picture can be seen in another stackoverflow article.

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][1]

.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][2]

[1]: http://jsfiddle.net/kq5Ef/ "LIVE DEMO" [2]: http://codepen.io/chriscoyier/pen/lotjh

Just to follow up on this - if you want the arrow to position itself correctly (like when using it on a navbar element that is right-aligned, you need the following additional CSS to ensure the arrow is right-aligned:

.navbar .navbar-right > li > .dropdown-menu:before,
.navbar .nav > li > .dropdown-menu.navbar-right:before {
    right: 12px; left: auto;
}

.navbar .navbar-right > li > .dropdown-menu:after,
.navbar .nav > li > .dropdown-menu.navbar-right:after {
    right: 13px; left: auto;
}

Note the "navbar-right" - that was introduced in BS3 instead of pull-right for navbars.

The CSS that Alexander Mistakidis provided is correct. Which is to say, it creates the arrow atop the dropdown menu in Bootstrap. In order to position it correctly in a responsive view (@user2993108), you can change the left attribute for each of the class selectors (.dropdown-menu:before,.dropdown-menu:after) at different media queries or breakpoints.

For example...

@media (max-width: 400px) {

.dropdown-menu:before {
  position: absolute;
  top: -7px;
  left: 30px; /* change for positioning */
  ...
}

.dropdown-menu:after {
  position: absolute;
  top: -6px;
  left: 31px; /* change for positioning */
  ...
}

}

@media (max-width: 767px) and (min-width: 401px) {

.dropdown-menu:before {
  position: absolute;
  top: -7px;
  left: 38px; /* change for positioning */
  ...
}

.dropdown-menu:after {
  position: absolute;
  top: -6px;
  left: 39px; /* change for positioning */
  ...
}

}

and so on...

This builds on the work by Alexander Mistakidis and Joyrex to support optional arrows and dropup menus. In my case I did not want to have an arrow on all of the dropdown menus, only some.

With this, you add the arrow class to the dropdown-menu element to get the arrow. If Bootstrap is positioning the dropdown/dropup to the left, also add arrow-right to shift the arrow to the other side.

// add an arrow to the dropdown menus
.dropdown-menu.arrow:before {
  position: absolute;
  left: 9px;
  display: inline-block;
  border-right: 7px solid transparent;
  border-left: 7px solid transparent;
  content: '';
}
.dropdown-menu.arrow:after {
  position: absolute;
  left: 10px;
  display: inline-block;
  border-right: 6px solid transparent;
  border-left: 6px solid transparent;
  content: '';
}

// postion at the top for a 'down' menu
.dropdown .dropdown-menu.arrow:before {
  top: -7px;
  border-bottom: 7px solid #ccc;
  border-bottom-color: rgba(0, 0, 0, 0.2);
}
.dropdown .dropdown-menu.arrow:after {
  top: -6px;
  border-bottom: 6px solid #ffffff;
}

// postion at the bottom for an 'up' menu
.dropup .dropdown-menu.arrow:before {
  bottom: -7px;
  border-top: 7px solid #ccc;
  border-top-color: rgba(0, 0, 0, 0.2);
}
.dropup .dropdown-menu.arrow:after {
  bottom: -6px;
  border-top: 6px solid #ffffff;
}

// support to move the arrow to the right-hand-side
.dropdown-menu.arrow.arrow-right:before,
.dropup .dropdown-menu.arrow.arrow-right:before {
  right: 15px;
  left: auto;
}
.dropdown-menu.arrow.arrow-right:after,
.dropup .dropdown-menu.arrow.arrow-right:after {
  right: 16px;
  left: auto;
}