Resolution problems on certain browsers

For some reason, my site is having resolution issues on certain browsers. Chrome is easily the best, followed by Firefox and then Safari, although I haven’t tried on multiple machines yet. Here are screenshots of the homepage on each browser:

Chrome: https://i.imgur.com/fnnRDkc.jpg
Firefox: https://i.imgur.com/Z1wOR74.jpg
Safari: https://i.imgur.com/l4PmbzX.jpg

Is this something that the theme developer would have to fix, or is there a quick solution that I could try to implement myself?

I know almost no one uses Safari, but it’d be nice to have the site looking nice across all browsers.