Edit in JSFiddle

<nav class="segmented">
  <input type="radio" name="seg-1" value="Organisation" id="seg-Organisation">
  <label for="seg-Organisation">Organisation</label>
  <input type="radio" name="seg-1" value="Users" id="seg-Users">
  <label for="seg-Users">Users</label>
  <input type="radio" name="seg-1" value="Units" id="seg-Units">
  <label for="seg-Units">Units</label>
  <input type="radio" name="seg-1" value="Tags" id="seg-Tags">
  <label for="seg-Tags">Tags</label>
</nav>

.segmented {
  padding: 12px;   
}
.segmented input[type=radio] {
   display: none;
}
.segmented label {
  border: outset 1px silver;
  padding: 2px 16px;
  margin-right: -5px;
  background: #ddd;
    cursor: pointer;
}

.segmented input:checked + label {
  border: inset 1px silver;   
  background: #aaa;
}