The changes that are important for using this theme for latest 2.3.0. I created separate part because this is needed for all my themes. Mainly for those with HTML layout.
The update is easy.
Use code from the bootstrap3 theme and adjust your theme code.
I left in this video the sync part too. I don’t know if this is a bug, or only it is because I use browser debugger and not developer mode, but I was surprised for the first time. Who likes fatal error just after the update, don’t they?
PS. I added source files after part 3 too.