When using vim-plug, add the following lines in your ~/.vimrc file:
call plug#begin('~/.vim/plugged')
Plug 'aristeo812/ob3-vim-syntax'
call plug#end()
Just copy the ftdetect and syntax folders in your ~/.vim directory.
The plugin would automatically detect Openbox theming file as a themerc file in an openbox-3 directory. If you want a more general approach, add the following line in your ~/.vimrc file:
autocmd BufRead,BufNewFile *themerc set filetype=ob3
Also, you can always set the desired filetype manually by entering the following command in vim:
set ft=ob3
The original author is Dave Foster. Modified by Victor Brand (Zhuravlev).