A CodePen by cole007. Centered DropDown Menu with CSS - Just another menu just with CSS3.

index.html

<div class="content">
  <h1>centered dropdown menu with css</h1>
  <div id="menu">
    <ul>
      <li class="active">
        <a href="#">Home</a>
      </li>
      <li>
        <a href="#">Blog</a>
      </li>
      <li>
        <a class="dropdown" href="#">Tutorials</a>
        <ul>
          <li>
            <a href="#">CSS</a>
          </li>
          <li>
            <a href="#">Illustrator</a>
          </li>
          <li>
            <a href="#">jQuery</a>
          </li>
          <li>
            <a href="#">Photoshop</a>
          </li>
          <li>
            <a class="dropright" href="#">Web Design</a>
            <ul>
              <li><a href="#">Articles</a></li>
              <li><a href="#">Snippets</a></li>
              <li><a href="#">Tips & Tricks</a></li>
            </ul>
          </li>
        </ul>
      </li>
      <li>
        <a class="dropdown" href="#">Freebies</a>
        <ul>
          <li><a href="">Icons</a></li>
          <li><a href="">Images</a></li>
          <li><a href="">Fonts</a></li>
          <li><a href="">PSDs</a></li>
          <li><a href="">Vectors</a></li>
        </ul>
      </li>
      <li>
        <a href="#">About</a>
      </li>
    </ul>
  </div>
  <p>Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo. Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo.</p>
  <p>Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo.</p>
</div>

style.less

/*****LESS*****/
.rounded(@radius:5px){
  -webkit-border-radius:@radius;
  -moz-border-radius:@radius;
  border-radius:@radius;
}
.boxShadow(@args){
  -webkit-box-shadow:~"@{args}";
  -moz-box-shadow:~"@{args}";
  box-shadow:~"@{args}";
}
.gradient(@start:#fff,@end:#000) {
  background-color: @start;
  background:-webkit-gradient(linear, left top, left bottom, from(@start), to(@end));
	background:-webkit-linear-gradient(top, @start, @end);
	background:-moz-linear-gradient(top, @start, @end);
	background:-ms-linear-gradient(top, @start, @end);
	background:-o-linear-gradient(top, @start, @end);
	background:linear-gradient(top, @start, @end);
	filter:progid:DXImageTransform.Microsoft.gradient(startColorStr="@{start}", EndColorStr="@{end}");
}
.textShadow(@args){
  -webkit-text-shadow:~"@{args}";
  -moz-text-shadow:~"@{args}";
  text-shadow:~"@{args}";
}
/**************/
html,body{
  background:#333;
}
.content{
  background:#fff;
  .rounded(1em);
  .boxShadow("0 20px 10px -15px rgba(0,0,0,.8)");
  margin:0 auto;
  padding:5px;
  width:70%;
  h1{
    font:bold 21px/1.5em sans-serif;
    margin:.5em 0;
    padding:0;
    text-align:center;
    .textShadow("0 1px 1px rgba(0,0,0,.5)");
    text-transform:uppercase;
  }
}
#menu{
  .gradient(#ddd,#999);
  .rounded;
  .boxShadow("0 10px 6px -6px rgba(0,0,0,.7)");
  display:inline-block;
  margin:10px 0 0;
  padding:0;
  position:relative;
  width:100%;
  z-index:900;
  ul{
    float:right;
    list-style:none;
    margin:0;
    padding:0;
    position:relative;
    right:50%;
    li{
      float:left;
      left:50%;
      margin:0;
      padding:0;
      position:relative;
      a{
        background:transparent;
        border-left:1px solid #888;
        border-right:1px solid #eee;
        color:#333;
        display:block;
        font:12px/1.5em "Verdana",sans-serif;
        margin:0;
        padding:5px 20px;
        text-decoration:none;
        .textShadow("0 1px 0 rgba(255,255,255,.7)");
        &.dropdown:after{
          content:"\25BC";
          padding-left:5px;
        }
        &.dropright:after{
          content:"\25BA";
          padding-left:5px;
        }
      }
      &:first-child{
        border-left:1px solid #eee;
      }
      &:last-child{
        border-right:1px solid #888;
      }
      &.active{
        a{
          .gradient(#fa6,#fe0);
          color:#000;
          .textShadow("0 1px 0 rgba(255,255,255,.5)");
        }
      }
      &:hover, &:focus{
        &>a{
          .gradient(#111,#555);
          color:#fff;
          .textShadow("0 1px 0 rgba(0,0,0,.7)");
        }
        &>ul{
          display:block;
        }
      }
    }
    ul{
      .boxShadow("0 0 10px rgba(0,0,0,.70)");
      display:none;
      left:0;
      position:absolute;
      right:auto;
      text-align:left;
      width:140px;
      li{
        border:0 !important;
        left:0;
        width:100%;
        a{
          .gradient(#ddd,#999);
          border:0 !important;
          margin:0;
          padding:5px;
        }
        &:hover{
          &>ul{
            display:block;
          }
        }
      }
      ul{
        display:none;
        position:absolute;
        left:140px;
        top:0;
      }
    }
  }
}