We completely redesigned the style system from LiveJournal's version, yes! You can technically create a custom style with the code from the base style of whatever LJ style you were using (don't ask me how to do it, honestly, I understand nothing about the style system, but there are instructions somewhere in style_system I think) but we very, very much do not recommend that you do that: a style that was written for LJ won't have access to any of the journal or style features we've added in the last 13 years, and may occasionally break because we've had to make changes to the style core. I very very very much recommend picking a native DW style and recreating the look of your old layout. Again, style_system is an unofficial comm but full of very helpful people!