2.5x3.5 in paper size

generator/css/card-size.css

     height: 278mm; /* full: 279.4mm (11.0in) */
 }
 
+page[size="25x35"] {
+    width: 63.6mm;
+    height: 89.0mm;
+}
+
 /* Default card size */
 .card {
     width:2.5in;

generator/generate.html

                             <select class="form-control" id="page-size" data-option="page_size">
                                 <option value="A4" selected>A4</option>
                                 <option value="Letter">US letter</option>
+                                <option value="25x35">2.5&quot; x 3.5&quot;</option>
                             </select>
                         </div>
                     </div>