AH! Got it!
This one will be part of the next theme update, so you can edit the theme’s style.css directly for this. Normally I would say create custom CSS, but here is the fix…
Open the theme’s style.css and look for this around line 173:
#masthead {
background-repeat:no-repeat;
background-size:auto;
background-position: center;
position: relative;
z-index:1;
}
Change the z-index: 1; to be z-index: 9999;
Now for a little recommendation…after looking at the slider you are using and the source code it generates, you may want to consider a more simplified slider if you just want to rotate images. I also noticed the code it inserts into your page content is not really the best way of doing it (which is what the slider does, not you) and it loads css styles in your content which is not a good practice. You might want to look at some other options:
Simple Responsive Slider
Meta Slider
Smart Slider 3 if you want more fancy.