bootstrap menu showing up blank/not able to style

bootstrap menu showing up blank/not able to style

Here's the markup for the dropdown-menu div:
<div class="btn-group-two">
<button class="btn dropdown-toggle" data-toggle="dropdown">
Action
<span class="caret white-caret"></span>
</button>
<ul id="menu" class="dropdown-menu">
<li>one</li>
<li>two</li>
<li>three</li>
</ul>
</div>
CSS:
.btn-group-two ul .dropdown-menu li a{
color: red;
}
What is the problem? something I'm missing? thx.