fix(style): workaround mobile browser issues with fixed bg

Revert the parallax-like fixed background effect on mobile to scroll based attachment.

wowchemy/assets/scss/wowchemy/_widgets.scss

@@ -76,10 +76,16 @@
   background-size: cover;
 }
 
-/* Create a parallax-like scrolling effect. */
+/* Create a parallax-like scrolling effect on desktop browsers. */
 .parallax {
   background-attachment: fixed;
 }
+// Workaround issue with mobile browser support for fixed parallax background.
+@media (min-width: 768px) {
+  .parallax {
+    background-attachment: scroll;
+  }
+}
 
 .home-section:first-of-type {
   padding-top: 50px;