The dark grey bar that holds the "Play"-Button on either the Bedrock and Dungeon, or the other way around (on Java and Legends), Play Page is off by maybe just one pixel. Either way, two of the Pages line up and the other two do not.

Screenshots show Java/Bedrock Page comparison. Pretty visible on the pointed at flowers.

Recreate: Open Launcher and switch between the Pages. It will be visible on all different window sizes i've tried.

(More a Design issue than an actual bug!)