Remove sidebars from mobile view

I’ve tried EVERYTHING that I’ve seen suggested on other posts and can’t seem to figure out how to do this. On my mobile device, my pages’ sidebars are coming up at the top rather than the actual content. I would like to just have NO sidebars show up on mobile devices to make this simpler.

I’ve seem some CSS code suggestions on other posts but nothing has worked for my site. My theme is Happy Kids but I don’t have access to their support because I purchased it so long ago.

Thank you!!

The page I need help with: [log in to see the link]