Welcome back @TW_user, is it easy to share the change you wanted to make, a solution may be easier than an an explanation.
But what do you mean by?;
- It may be better to make a bundle of tiddlers and transfering them to you new wiki.
A solution?
Possibly the best way to introduce CSS changes is to put the change in a tiddler tagged $:/tags/Stylesheet then the latest wins. See Control Panel > Info > Advanced > StyleSheets for the order that results. Bottom is the last, that wins. Because I expect it is subsequently overridden.
The explanation?
You will see that $:/boot/boot.css is not in the list of stylesheets and is not a shadow tiddler in the $:/core, although it is mentioned, this needs a little deeper investigation.
- So to fully understand, you need to uncover the role of boot.css in the boot process or use a more “standard solution” as mentioned above.
- $:/boot/boot.css says “Basic styles used before we boot up the parsing engine” so I would not rely on this post "boot up"
- See the Dev Tiddlywiki for more info BootMechanisium
Let us know if the solution above works and you really want to dig deeper.