vertical scroll for source-code on small devices

doc/jekyll/css/tabs.css

@@ -53,6 +53,16 @@ input:checked + label {
 	padding: 0.5em;
 	position: absolute;
 	z-index: -100;
+	border-color: #333;
+	border-width: 1px;
+}
+
+.highlighter-rouge {
+	overflow-x: auto;
+}
+
+.highlighter-rouge pre {
+    min-width: 662px;
 }
 
 #content #content1 {