Since Tiki 13 our Smarty templates changed to produce Bootstrap compatible HTML. Since Tiki 14 our theme system was completely rewritten so instead styles/ and separate templates/ folders all the themes reside in themes/ folder now.
Every developer should make sure that Tiki produces valid HTML5 and check if the structure is Bootstrap compatible.
Here are some tools:
- Tiki's CSS and Smarty template organization
- https://themes.tiki.org/Template+Tricks (some info might be outdated)