[GoDark] Post Design

[WallBB]

Hey mzm,
You can do that using classic postbit, ofcourse to make it similar you will need to do custom edits to your postbit_classic template.
You can change postbit_classic template for your account using

-> YOURFORUM/usercp.php?action=options
Thread View Options > Display posts in classic mode (Select this)

To set it as default , set this option in Admin CP

ACP -> Settings -> Showthread Options. Select classic view

And for existing users, check this tutorial
https://community.mybb.com/thread-40093.html

Regards
WallBB