For added comment, with regard to broken graphic links in the demo data, there are 119 broken links.
Failed to load resource: net::ERR_NAME_NOT_RESOLVED
Most with this URL, just different graphic names (.jpg and .png):
http://demo-data.demo.styledthemes.com/flat-responsive/wp-content/uploads/2016/01/gallery_two_6.jpg
The widget_banner_position item, in code, is within the div class=”textwidget”
img src=”http://demo-data.demo.styledthemes.com/flat-responsive/wp-content/uploads/2016/01/banner_wide.jpg” title=”widget_banner_position”
After changing the Banner Wide widget, under Widgets of the theme customization settings, THAT is actully mobile friendly.
img src=”http://www.mywebsite.org/wp-content/uploads/2017/03/2.jpg” title=”widget_banner_position”
Establishing a header image under Header Image in the customization settings does not appear to be mobile friendly and is gawdawful large, taking up quite a bit of real estate on mobile.
I hope these notes are useful to others using this theme.