Fix event listeners assignation

static/canvas.js

@@ -154,8 +154,8 @@ window.addEventListener('load', function() {
 
   // Add event listeners to inputs
   let inputs = document.querySelectorAll('.colorpicker input[type="radio"], #step3 input[type="radio"], #step4 input[type="radio"]');
-  for (let i = 0; i < bgColorElems.length; ++i) {
-    bgColorElems[i].onchange = draw;
+  for (let i = 0; i < inputs.length; ++i) {
+    inputs[i].onchange = draw;
   }
   document.getElementById('step2value').oninput = draw;
   document.getElementById('signature').oninput = draw;