Reply To: Change Content & Sidebar Width

“If you are changing this with your browser via something like firebug it works fine. But if you add your own custom CSS (like through the customizer), it does not work properly.”

The CSS will definitely work on both Firebug and the customizer. If you add it to the customizer or the style.css file directly you just need to make sure you clear your browser cache so the site shows your latest changes. Hit your Reload button and it should do it automatically.

BTW, your link doesn’t appear to be working.