Header Not Responsive For Mobile Viewing

My header looks great on desktop, however it looks very poor on mobile. Based on my research, I’m thinking that it’s because it is not responsive. It’s strange because on one of the pages (About Us), it looks perfectly fine, but on every other page of the website, it does not. When I preview “Mobile” on my desktop, each page looks perfectly fine as well, but on my actual phone the header is messed up on every page except the About Us page. I’ve tried inputting suggested CSS codes, but it doesn’t work; though I may not be putting it in the correct place because I don’t have any knowledge on CSS. Please help! FYI: My theme is Flash Blog.

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