How do I add space between the blocks inside a Container?

Open the Container in the page editor. At the top of its Content tab, Space Between Blocks sets the room between the blocks inside it: under each block in a stack, and between blocks that sit side by side. Choose None, Small, Medium, or Large.

None keeps the blocks close together, which is how every Container looked before this setting existed. Phones stack the blocks in one column with their own spacing whichever you choose.