Combo classes overide on all devices

Hi. So I am following a course on webflow. I have to set up mobile design now.
I have to select Section in styles and add one more mobile overflow combo section to it, so it doesnt change on all devices.
I do that, and instantly, i get that combo section to all devices. And it affects all devices.
As i understood and from my previous classes, when i give a combo class, that class is only changing that device i am working on, where i gave that specific combo class.

What am i doing wrong?

That’s not how css works. Combo classes affects everything from top to down. It’s with breakpoints that you add different style for different devices, but still with a top-down approach. Desktop modifications are visibile even on mobile, mobile modifications are visibile only on mobile