Add background to the whiteboard app

www/whiteboard/index.html

@@ -20,6 +20,10 @@
         body {
             display: flex;
             flex-flow: column;
+            height: 100%;
+            background: url('/customize/bg3.jpg') no-repeat center center;
+            background-size: cover;
+            background-position: center;
         }
         textarea{
             width: 100%;
@@ -36,9 +40,14 @@
             /* disallow textarea resizes */
             resize: none;
         }
+        #canvas-area {
+            flex: 1;
+            display: flex;
+        }
         .canvas-container {
             border: 5px solid black;
             margin: auto;
+            background: white;
         }
         #clear {
             display: inline;
@@ -62,6 +71,7 @@
             display: block;
             position: relative;
             border: 3px solid black;
+            background: white;
         }
         #width, #colors {
             position: relative;