Simple, not very styled, CSS only cross browser dropdown menu sass/scss mixin.

dropdown-menu.scss

// Sort of based on http://matthewjamestaylor.com/blog/centered-dropdown-menus
// but with centering elements removed.

@mixin navmenu($z-index, $width) {

  clear: both;
  float: left;
  margin: 0;
  padding: 0;
  width: 100%;
  z-index: $z-index;
  position: relative;

  ul {
    margin: 0;
    padding: 0;
    list-style: none;
    float: right;
    position: relative;
    li {
      margin: 0 0 0 1px;
      padding: 0;
      float: left;
      position: relative;
      top: 1px;
      a {
        display: block;
        margin: 0;
        padding: .6em .5em .4em;
      }
      &:last-child ul {
        left: auto;
        right: 0;
        text-align: right;
      }
      &:hover ul { display: block; }
    }
    ul {
      display: none;
      position: absolute;
      top: 2em;
      left: 0;
      right: auto;
      width: $width;
      li {
        left: auto;
        margin: 0;
        clear: left;
        width: 100%;
        a, &:hover ul li a {
          background: #eee;
          color: #444;
          line-height: 1.4em;
        }
        a:hover, &:hover ul li a:hover {
          background: #ddd;
          color: $hover-color;
        }
      }
    }
  }

}