When designing mobile and desktop versions of a funnel, it is best to create mobile-only and desktop-only sections. This will hide entire sections depending on the device so that you can have dramatic differences and keep everything looking clean at all sizes.
NOTE: Font sizes are the only elements that can have simultaneous settings (desktop font size and mobile font size).
Layout, spacing, and other structural changes require mobile-only and desktop-only sections. As such, the recommendation is to build out the desktop version first and then in mobile view, determine which sections don't show up how you want them to. Once you've determined those sections, you can duplicate them, change one version to desktop only (see steps below) and the other to mobile only. You'll then be able to edit the mobile only as needed.
To do have a section be desktop only or mobile only, follow these simple steps:
Step 1: Click the Edit icon on the funnel of your choice.
Step 2: Click the yellow "Edit Page" button.
Step 3: Click on the element you want to edit.
Step 4: Under "Section Settings" > "Advanced".
Step 5: Under "Visibility", click on the desktop and mobile icons until blue to turn them on.
Step 6: Then, in the top menu bar, you can click the same desktop and mobile icons to view the optimized pages.
Step 7: Be sure to save changes before exiting!