Custom CSS + the Classify plugin by @julienallard1.
The .main-page part makes the whole page fit to the height of the viewport
The .full-height class you put on any specific element that you want to also want as 100% height of it’s container. (You’ll need to use Classify to do this)
(this is just a (hidden) HTML element with a height and width of 1)
Not sure what is on @Bubble’s roadmap but full height pages seem like a pretty standard thing for websites cc @allenyang