Put all your elements on a page in a View element (group) and when you've done enough UI design on a page copy the View and paste it on a new page as a backup.
A corollary to the Bulk copy and paste trick is this backup tip.
Since we don't currently have undo/redo in the editor, it is always a good idea to have a backup copy of pages that you have spent some time designing the UI.
There are many times when i'm debugging i end up having to delete some elements just to find a problem and i don't want to spend time redoing them again.
Also if you mistakenly delete a view, especially if you have all your page elements in one top-level view, you can always go to your backup.
Of course copying and pasting a view/elements wont copy their workflows (even and actions). Hey @Dropsource here is a feature request, please give us ability to copy and paste an element with its events and actions. Bubble does this and it's supper helpful.
As a general advice from my own experience, with the current state of Dropsource, don't start your app by spending most of your time on the UI. You may end up mistakenly deleting something, intentionally deleting something for debugging or even changing your mind. So focus on the functionality, interaction and connectivity with your backend. Once you have that knocked down you can then make your pages look beautiful by styling it.