code-pen-awesome-tag.html

<div class="container">
  <ul class="tags">
    <li><a href="#">Interface <span>4</span></a></li>
    <li><a href="#">Icon <span>8</span></a></li>
    <li><a href="#">Typography <span>15</span></a></li>
    <li><a href="#">Color <span>16</span></a></li>
  </ul>

  <ul class="tags green">
    <li><a href="#">Design <span>23</span></a></li>
    <li><a href="#">Illustration <span>42</span></a></li>
    <li><a href="#">Component <span>108</span></a></li>
    <li><a href="#">Misc <span>12</span></a></li>
  </ul>

  <ul class="tags blue">
    <li><a href="#">Infrastructure <span>31</span></a></li>
    <li><a href="#">Application <span>33</span></a></li>
    <li><a href="#">Mobile <span>65</span></a></li>
    <li><a href="#">Desktop <span>160</span></a></li>
  </ul>
</div>

style.css

/*
 * Copyright (c) 2012 Thibaut Courouble
 * http://www.webinterfacelab.com
 * Licensed under the MIT License
 *
 * Sass/SCSS source: http://goo.gl/AU3vR
 */

body {
  font: 13px/20px "Lucida Grande", Tahoma, Verdana, sans-serif;
  color: #404040;
  background: #eee;
}

.container {
  margin: 50px auto;
  width: 380px;
}

.tags {
  zoom: 1;
}

.tags:before, .tags:after {
  content: '';
  display: table;
}

.tags:after {
  clear: both;
}

.tags li {
  position: relative;
  float: left;
  margin: 0 0 8px 12px;
}

.tags li:active {
  margin-top: 1px;
  margin-bottom: 7px;
}

.tags li:after {
  content: '';
  z-index: 2;
  position: absolute;
  top: 10px;
  right: -2px;
  width: 5px;
  height: 6px;
  opacity: .95;
  background: #eb6b22;
  border-radius: 3px 0 0 3px;
  -webkit-box-shadow: inset 1px 0 #99400e;
  box-shadow: inset 1px 0 #99400e;
}

.tags a, .tags span {
  display: block;
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  box-sizing: border-box;
}

.tags a {
  height: 26px;
  line-height: 23px;
  padding: 0 9px 0 8px;
  font-size: 12px;
  color: #555;
  text-decoration: none;
  text-shadow: 0 1px white;
  background: #fafafa;
  border-width: 1px 0 1px 1px;
  border-style: solid;
  border-color: #dadada #d2d2d2 #c5c5c5;
  border-radius: 3px 0 0 3px;
  background-image: -webkit-linear-gradient(top, #fcfcfc, #f0f0f0);
  background-image: -moz-linear-gradient(top, #fcfcfc, #f0f0f0);
  background-image: -o-linear-gradient(top, #fcfcfc, #f0f0f0);
  background-image: linear-gradient(to bottom, #fcfcfc, #f0f0f0);
  -webkit-box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.7), 0 1px 2px rgba(0, 0, 0, 0.05);
  box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.7), 0 1px 2px rgba(0, 0, 0, 0.05);
}

.tags a:hover span {
  padding: 0 7px 0 6px;
  max-width: 40px;
  -webkit-box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.15), 1px 1px 2px rgba(0, 0, 0, 0.2);
  box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.15), 1px 1px 2px rgba(0, 0, 0, 0.2);
}

.tags span {
  position: absolute;
  top: 1px;
  left: 100%;
  z-index: 2;
  overflow: hidden;
  max-width: 0;
  height: 24px;
  line-height: 21px;
  padding: 0 0 0 2px;
  color: white;
  text-shadow: 0 -1px rgba(0, 0, 0, 0.3);
  background: #eb6b22;
  border: 1px solid;
  border-color: #d15813 #c85412 #bf5011;
  border-radius: 0 2px 2px 0;
  opacity: .95;
  background-image: -webkit-linear-gradient(top, #ed7b39, #df5e14);
  background-image: -moz-linear-gradient(top, #ed7b39, #df5e14);
  background-image: -o-linear-gradient(top, #ed7b39, #df5e14);
  background-image: linear-gradient(to bottom, #ed7b39, #df5e14);
  -webkit-transition: 0.3s ease-out;
  -moz-transition: 0.3s ease-out;
  -o-transition: 0.3s ease-out;
  transition: 0.3s ease-out;
  -webkit-transition-property: padding, max-width;
  -moz-transition-property: padding, max-width;
  -o-transition-property: padding, max-width;
  transition-property: padding, max-width;
}

.green li:after {
  background: #65bb34;
  -webkit-box-shadow: inset 1px 0 #3a6b1e;
  box-shadow: inset 1px 0 #3a6b1e;
}

.green span {
  background: #65bb34;
  border-color: #549b2b #4f9329 #4b8b27;
  background-image: -webkit-linear-gradient(top, #71ca3f, #5aa72e);
  background-image: -moz-linear-gradient(top, #71ca3f, #5aa72e);
  background-image: -o-linear-gradient(top, #71ca3f, #5aa72e);
  background-image: linear-gradient(to bottom, #71ca3f, #5aa72e);
}

.blue li:after {
  background: #56a3d5;
  -webkit-box-shadow: inset 1px 0 #276f9e;
  box-shadow: inset 1px 0 #276f9e;
}

.blue span {
  background: #56a3d5;
  border-color: #3591cd #318cc7 #2f86be;
  background-image: -webkit-linear-gradient(top, #6aaeda, #4298d0);
  background-image: -moz-linear-gradient(top, #6aaeda, #4298d0);
  background-image: -o-linear-gradient(top, #6aaeda, #4298d0);
  background-image: linear-gradient(to bottom, #6aaeda, #4298d0);
}