Minecraft: Java Edition Snapshot 21w41a brings a new background image and lots of fixes
The latest Minecraft: Java Edition snapshot is now available to testers, and includes a fresh batch of fixes and tweaks for 1.18 'Caves and Cliffs Update' Part Two. However, this snapshot also updates the background image for the main menu to match the Caves and Cliffs Update, which is a small but important milestone during development.
Source: windowscentral.com