Add the ability to move a breakpoint-specific layout or style setting up or down the breakpoint hierarchy. 

This can be done in the pop-up that appears when you click blue breakpoint-specific style settings, 

e.g. button options-

1. Remove this style
2. Move this style up to the "Tablet" breakpoint.
3. Move this style down to the "Mobile - Portrait" breakpoint.
4. OK

In cases where you will be overwriting a style-setting at that specific breakpoint, you could alert and request confirmation.

WHY THIS WOULD HELP

When styling an element at e.g. the "Tablet" breakpoint, I might discover that style setting works better at the "Desktop" level, or at the "Mobile - Landscape" level. 

Currently the only option is to delete all of the styling and then recreate it at the desired level - slow, painful, and error-prone.

MORE ADVANCED APPROACH

A more advanced version would display all of the breakpoint-specific style settings for that item, as a list - so that you can easily drag-move those style settings higher or lower in the breakpoint settings.