Edit in JSFiddle

JavaScript
HTML
CSS
Result

<div class="glossy-selectbox">
    <input type="checkbox">
    <label data-default="Compartilhe este artigo!" data-focus="Escolha um dos serviços de mídia social ..."></label>
    <ul>
        <li><a class="social-rss" href="AQUI A URL" target="_blank">RSS Feed</a></li>
        <li><a class="social-facebook" href="AQUI A URL" target="_blank">Facebook</a></li>
        <li><a class="social-twitter" href="AQUI A URL" target="_blank">Twitter</a></li>
        <li><a class="social-google" href="#AQUI A URL" target="_blank">Google+</a></li>
    </ul>
</div>

<div class="glossy-selectbox">
    <input type="checkbox">
    <label data-default="Compartilhe este artigo!" data-focus="Escolha um dos serviços de mídia social ..."></label>
    <ul>
        <li><a class="social-rss" href="http://feeds.feedburner.com/mult-focos" target="_blank">RSS Feed</a></li>
        <li><a class="social-facebook" href="https://www.facebook.com/pages/Mult-focos/1432542490311026" target="_blank">Facebook</a></li>
        <li><a class="social-twitter" href="https://twitter.com/multfocos" target="_blank">Twitter</a></li>
        <li><a class="social-google" href="https://plus.google.com/u/0/107868990022648564296/about" target="_blank">Google+</a></li>
    </ul>
</div>

/*
 * Drop Down Menu para compartilhar Mídia Social
 * Mult-focos
 * URL: https://plus.google.com/u/0/107868990022648564296/about
 */

.glossy-selectbox {
  display:inline-block;
  font:normal bold 12px Arial,Sans-Serif;
  position:relative;
  width:300px;
  background-color:#348EB7;
  text-align:left;
  /* CSS3 Browser */
  background-image:-webkit-linear-gradient(top,rgba(255,255,255,.4) 0%,rgba(255,255,255,.2) 50%,rgba(255,255,255,0) 50%,rgba(255,255,255,.1) 100%);
  background-image:-moz-linear-gradient(top,rgba(255,255,255,.4) 0%,rgba(255,255,255,.2) 50%,rgba(255,255,255,0) 50%,rgba(255,255,255,.1) 100%);
  background-image:-ms-linear-gradient(top,rgba(255,255,255,.4) 0%,rgba(255,255,255,.2) 50%,rgba(255,255,255,0) 50%,rgba(255,255,255,.1) 100%);
  background-image:-o-linear-gradient(top,rgba(255,255,255,.4) 0%,rgba(255,255,255,.2) 50%,rgba(255,255,255,0) 50%,rgba(255,255,255,.1) 100%);
  background-image:linear-gradient(top,rgba(255,255,255,.4) 0%,rgba(255,255,255,.2) 50%,rgba(255,255,255,0) 50%,rgba(255,255,255,.1) 100%);
  /* IE only */
  filter:progid:DXImageTransform.Microsoft.gradient(gradientType=0,startColorstr='#00688B',endColorstr='#3489B3');
  -webkit-border-radius:7px;
  -moz-border-radius:7px;
  border-radius:7px;
  -webkit-box-shadow:inset 0 1px 1px 1px rgba(255,255,255,.1),0 1px 3px rgba(0,0,0,.7);
  -moz-box-shadow:inset 0 1px 1px 1px rgba(255,255,255,.1),0 1px 3px rgba(0,0,0,.7);
  box-shadow:inset 0 1px 1px 1px rgba(255,255,255,.1),0 1px 3px rgba(0,0,0,.7);
}

.glossy-selectbox:before,
.glossy-selectbox:after {
  content:"";
  display:block;
  width:0;
  height:0;
  border:3px solid transparent;
  border-width:5px 3px;
  border-bottom-color:#00FFFF;
  position:absolute;
  top:25%;
  right:5px;
  z-index:4;
}

.glossy-selectbox:after {
  border-color:#00FFFF transparent transparent;
  top:auto;
  bottom:25%;
}

.glossy-selectbox input {
  display:block;
  position:absolute;
  top:0;
  right:0;
  bottom:0;
  width:15px;
  height:100%;
  opacity:0;
  z-index:10;
  cursor:pointer;
}

.glossy-selectbox label {
  display:block;
  line-height:45px;
  color:rgba(255,255,255,.5);
  padding:0 15px;
  -webkit-transition:all 0s ease-out;
  -moz-transition:all 0s ease-out;
  -ms-transition:all 0s ease-out;
  -o-transition:all 0s ease-out;
  transition:all 0s ease-out;
}

.glossy-selectbox label:before {
  content:attr(data-default);
}

.glossy-selectbox label:after {
  content:"";
  display:block;
  position:absolute;
  top:0;
  right:0;
  bottom:0;
  width:15px;
  border-left:1px solid rgba(0,0,0,.4);
  -webkit-border-radius:0 7px 7px 0;
  -moz-border-radius:0 7px 7px 0;
  border-radius:0 7px 7px 0;
  -webkit-box-shadow:inset 1px 0 0 rgba(255,255,255,.1),-1px 0 0 rgba(255,255,255,.1);
  -moz-box-shadow:inset 1px 0 0 rgba(255,255,255,.1),-1px 0 0 rgba(255,255,255,.1);
  box-shadow:inset 1px 0 0 rgba(255,255,255,.1),-1px 0 0 rgba(255,255,255,.1);
}

.glossy-selectbox input:hover + label {
  color:Cyan;
}

.glossy-selectbox input:hover + label:after {
  background-color:rgba(255,255,255,.04);
}

.glossy-selectbox ul {
  margin:0 0;
  padding:0 0;
  position:absolute;
  top:100%;
  left:14px;
  right:14px;
  background-color:#3487B1;
  border:1px solid #49B5D4;
  -webkit-box-shadow:0 1px 2px rgba(0,0,0,.4),0 5px 7px -2px rgba(0,0,0,.4);
  -moz-box-shadow:0 1px 2px rgba(0,0,0,.4),0 5px 7px -2px rgba(0,0,0,.4);
  box-shadow:0 1px 2px rgba(0,0,0,.4),0 5px 7px -2px rgba(0,0,0,.4);
  visibility:hidden;
  opacity:0;
  z-index:99;
}

.glossy-selectbox li {
  margin:0 0;
  padding:0 0;
  list-style:none;
  float:left;
  width:50%;
  display:inline;
}

.glossy-selectbox a {
  display:block;
  position:relative;
  color:#fff;
  text-decoration:none;
  text-shadow:0 0 2px Cyan;
  line-height:30px;
  border-top:1px solid #49B5D4;
  border-right:1px solid #49B5D4;
  padding:0 15px 0 32px;
  -webkit-box-shadow:inset 0 0 0 1px #104E8B;
  -moz-box-shadow:inset 0 0 0 1px #104E8B;
  box-shadow:inset 0 0 0 1px #104E8B;
  /*Nota Opera: Uma caixa de sombra instável irá aparecer se você não definir o raio de fronteira a menos de 1 pixel. Estranho! */
  -webkit-border-radius:1px;
  -moz-border-radius:1px;
  border-radius:1px;
}

.glossy-selectbox a:nth-child(even) {
  border-right-width:0;
}

CSS

.glossy-selectbox a:before {
  content:"";
  display:block;
  width:16px;
  height:16px;
  position:absolute;
  top:7px;
  left:7px;
  background-color:transparent;
  background-repeat:no-repeat;
  background-position:50% 0;
}

.glossy-selectbox a:hover:before {
  background-position:50% 100%;
}

.glossy-selectbox .social-rss:before      {background-image:url('img/social_rss.png');}
.glossy-selectbox .social-facebook:before {background-image:url('img/social_facebook.png');}
.glossy-selectbox .social-twitter:before  {background-image:url('img/social_twitter.png');}
.glossy-selectbox .social-google:before   {background-image:url('img/social_google.png');}

.glossy-selectbox a:hover {
  background-color:rgba(0,0,0,.2);
  color:#ccc;
}

/* On click, then... */
.glossy-selectbox input:checked + label {
  color:rgba(255,255,255,.4);
  -webkit-transition-duration:.4s;
  -moz-transition-duration:.4s;
  -ms-transition-duration:.4s;
  -o-transition-duration:.4s;
  transition-duration:.4s;
}

.glossy-selectbox input:checked + label:before {
  content:attr(data-focus);
}

.glossy-selectbox input:checked + label:after {
  background-color:rgba(0,0,0,.2);
  -webkit-box-shadow:inset 1px 0 1px rgba(0,0,0,.4),-1px 0 0 rgba(255,255,255,.1);
  -moz-box-shadow:inset 1px 0 1px rgba(0,0,0,.4),-1px 0 0 rgba(255,255,255,.1);
  box-shadow:inset 1px 0 1px rgba(0,0,0,.4),-1px 0 0 rgba(255,255,255,.1);
}

.glossy-selectbox input:checked ~ ul {
  visibility:visible;
  opacity:1;
}