Hi Mohammad,
Jeremy, used an early version of bootstrap for an very early version of tiddlywiki. .. The main problem with those frameworks, is that they are opinionated. ... So if you want to create your own idea, they all step on your feets. ...
That's why it was completely removed. It caused more troubles, than it solved. .. just to let you know!
TW uses normalize.css v3.0.0, which is MIT licensed as a reset module: $:/themes/tiddlywiki/vanilla/reset ... To deal with the different "browser quirks". !!! Check for duplicates !!!
The rest of TW definitiions are defined with base styles. $:/themes/tiddlywiki/vanilla/base
The other themes are built on top of base and just modifiy aspects, that they want to have different.
TiddlyWikis UI elements are all based on "tc-" prefixed settings. ... To map those tc- settings into other frameworks will be some "heavy duty" ... It's possible, but it will also cause some headaches, here and there.
have fun!
mario