The style change you experience is due to theme responsive design. You are basically previewing a tablet screen size view.
The responsive screen size breakpoints have changed in version 1.4.0 of the theme to be compatible with as many tablet devices and their screen sizes as possible.
I understand, the 1280px screen may still display the desktop theme layout perfectly fine. So, if you want to change it to previous value, please change the 1280px to 1200px on line number 1772 in style.css file of the theme. I will consider updating this in the next theme version too.