All themes missing header graphic when viewed on a tablet

I'm interested in possibly purchasing a theme as SMThemes has the nicest layouts I've seen so far; however the responsive code seems to be missing or not properly coded. When viewing the demos for each theme on a tablet, the main header graphic is missing and at times the text in the body paragraphs loses its formatting. Is there a solution to this issue?

Hi!
Our themes are provides "as is". To change the background you may need to edit the file style.css, css-->index.css/mobile.css/tablet.css/wide.css. We don't provide any services for editing themes for individual users.
Please, clarify the issue on formatting text?