Minecraft wiki entry for Development_versions, associated text: Redesigned how effects look in the inventory screen.
Can display while recipe book is showing.
The list of effects are now shown to the right of the player's inventory, instead of the left side.
When the inventory effects list is visible, it will be hidden from the game view to reduce screen clutter.
There’s now two modes of seeing the effect list: compact and classic:
Classic is the pre-existing list of effects, one after another.
Compact is a single icon for each effect, suitable for small screen estate.
The game will automatically switch between the two looks to suit the available screen estate.