This is a customized version of the Curves UI 1.9 theme for MyBB 1.8, originally created by MattyWjeisz as a tribute to Justin’s official MyBB 1.9 design.
I’ve taken the original responsive layout and made some layout and visual improvements to better fit a modern forum feel, while staying true to the original design language.
Changes in this version:

• Categories on the index are now displayed as styled cards with gradient headers
  
• Forum view and thread view pages are wrapped in matching card layouts for consistency
  
• Next/Previous thread navigation has been cleaned up with improved styling
  
• Removed the thread-level search bar for a more minimal layout
  
• Adjusted spacing, padding, and structure for better visual balance
  

This version is being shared for free, and all credit for the original theme goes to MattyWjeisz, effone, and of course Justin Soltesz for the foundation and inspiration behind MyBB 1.9’s design direction.
You can use this as-is or build on it further.

You can change gradient color for each fid by viewing global.css and looking for /* Unique gradient per category */

Link to the original theme is here