adding a previous button

static/css/screens.css

@@ -22,5 +22,5 @@ input.button{
 	display: inline-block;
 	font-size: 100%;
 	padding:1em;
-	margin:2em;
+	margin:2em 0;
 }

templates/x-dex.html

@@ -104,6 +104,7 @@
 					</tr>
 				</tbody>
 			</table>
+			<input class="button" type="button" onclick="prevScreen('choose','intro')" value="previous">
 			<input class="button" type="button" onclick="nextScreen('choose','identify')" value="next">
 		</div>
 		<!-- ********************* -->
@@ -124,6 +125,7 @@
 					</tr>
 				</tbody>
 			</table>
+			<input class="button" type="button" onclick="prevScreen('identify','choose')" value="previous">
 			<input class="button" type="button" onclick="nextScreen('identify','operate')" value="next">
 		</div>
 		<!-- ********************* -->
@@ -150,6 +152,7 @@
 				</div>			
 			</div>
 			<br>
+			<input class="button" type="button" onclick="prevScreen('operate','identify')" value="previous">
 			<input class="button" type="button" onclick="nextScreen('operate','describe')" value="next">
 		</div>
 		<!-- ********************* -->
@@ -163,6 +166,7 @@
 					</tr>
 				</tbody>
 			</table>
+			<input class="button" type="button" onclick="prevScreen('describe','operate')" value="previous">
 			<input class="button" type="button" onclick="nextScreen('describe','share')" value="next">
 		</div>
 		<!-- ********************* -->
@@ -188,5 +192,9 @@
     	document.getElementById(current).style.display = 'none';
     	document.getElementById(next).style.display = 'block';
     }
+	function prevScreen(current, previous) {
+    	document.getElementById(current).style.display = 'none';
+    	document.getElementById(previous).style.display = 'block';
+    }
 </script>
 {% endblock %}