[Theme: Evolve] Header image being cut off in mobile version

Hello,

I am using the evolve free theme. My header image is being majorly cut off in the mobile version. I read on some posts that this is because the headers are actually background images and are not responsive by default. I found and tried a few different CSS codes by going to appearance > customize > custom CSS, which just gives you a little box to paste code into. Not sure if this is where I was supposed to put it since Im not very familiar with coding and editing CSS, but nothing I have done has worked. Any help would be much appreciated.

Also a couple of images in my bootstrap slider are upside down on the mobile site, any ideas whats up with this?

Thanks!