Header Graphic Issues on small screens

Greetings,

I wanted to have a full graphical header and used the following topic as an instruction to do it:

https://hb-themes.com/forum/all/topic/working-with-header-graphics/

It looks great on desktop and landscape tablets, but anything under that and the graphic overflows from the header area and screws up the page. Is there a way to have a graphical header that works on all devices?

My site: http://getyourwebsiteonline.com/grayds/

Even the site in the topic that I linked to above is having this issue as well when I looked at it on my smartphone.