MC-3700: Create concept for background image style generation

- Fix mobile breakpoint width

Author: davemacaulay

app/code/Magento/PageBuilder/etc/view.xml

@@ -24,7 +24,7 @@
     </media>
     <vars module="Magento_PageBuilder">
         <var name="breakpoints">
-            <var name="mobile">767px</var>
+            <var name="mobile">768px</var>
         </var>
     </vars>
 </view>