body {
  background-color: #eee;
}

h1 {
  text-align: center;
}

.container {
  margin: 0 auto;
  width: 690px;
}

.tab {
  background-color: #fff;
  -webkit-box-shadow: 0 0 8px rgba(0, 0, 0, .16);
          box-shadow: 0 0 8px rgba(0, 0, 0, .16);
}

.tab_nav ul {
  overflow: hidden;
  margin: 0;
  padding: 0;
  list-style: none;
}

.tab_nav li {
  float: left;
  -webkit-box-sizing: border-box;
          box-sizing: border-box;
  margin: 0;
  width: 33.33333%;
  text-align: center;
}

.tab_nav li + li {
  border-left: 1px solid #666;
}

.tab_nav a {
  position: relative;
  display: block;
  padding: 1em;
  background-color: #212121;
  color: #666;
  text-decoration: none;
  -webkit-transition: all ease-in-out .3s;
  transition: all ease-in-out .3s;
}

.tab_nav a:after {
  position: absolute;
  right: 0;
  bottom: -3em;
  left: 0;
  margin: 0 auto;
  width: 1em;
  height: 1em;
  background-color: #fff;
  content: '';
  -webkit-transition: all ease-in-out .3s;
  transition: all ease-in-out .3s;
  -webkit-transform: rotate(-45deg);
      -ms-transform: rotate(-45deg);
          transform: rotate(-45deg);;
}

.tab_nav a:hover {
  background-color: #333;
  color: #fff;
}

.tab_nav .is-active {
  background-color: #212121;
  color: #fff;
}

.tab_nav .is-active:after {
  bottom: -.5em;;
}

.tab_content {
  padding: 1em;
}