Add tabs to style guide

app/assets/stylesheets/content/_tabs.lsg

@@ -0,0 +1,26 @@
+# Scrollable tabs
+
+```
+<div #scrollContainer class="scrollable-tabs">
+  <ul #scrollPane class="tabrow"">
+    <li selected="true"
+        tab-id="tab_1">
+      <a href="#scrollable-tabs?tab=tab_1" textContent="Tab 1">Tab 1</a>
+    </li>
+    <li selected="false"
+        tab-id="tab_2">
+      <a href="#scrollable-tabs?tab=tab_2" textContent="Tab 2">Tab 2</a>
+    </li>
+    <li selected="false"
+        tab-id="tab_3">
+      <a href="#scrollable-tabs?tab=tab_3" textContent="Tab 3">Tab 3</a>
+    </li>
+  </ul>
+  <div #scrollLeftBtn hidden="true" class="scrollable-tabs--button -left">
+    <span class="icon-arrow-left2"></span>
+  </div>
+  <div #scrollRightBtn hidden="true" class="scrollable-tabs--button -right">
+    <span class="icon-arrow-right2"></span>
+  </div>
+</div>
+```