User Control Panel -> Board preferences -> My board style: ORP Legacy (Bolt)
UserCSS style for the forum that tries to imitate the main theme of the I/O website, to some extent.
Was made for my own use last month, now published. How it usually goes.
Original "Bolt" Grav theme by Marv. Some css code is being used from there to match the look.
Only outer section and main navigation bar is modified, hence base in the title.