Is global the right way to go?

[mdpotter55]

This could be done with a wrapping element that does not affect the dom's structure beyond css. A mix of setProperty() and removeProperty() could be used to handle the theme transitions.

I do like your object storage for variable settings. A lot cleaner than what I was working on.

Possible benefits: Global default variables could be defined in script to handle non-js systems. (rare to be sure) -- global defaults also allow for partial rewrites of the variables. (i.e. no need to rewrite media breakpoints unless desired.)
Applying to a wrapping element allows for the nesting of variable settings. Perhaps modals look different.
Named wrappers could still use localStorage for defaults. This allows for easier real-time changes with user-defined themes. Property setters make the code cleaner since you don't have to build complex strings beyond your tiered variable names.

Listed below is a simple example. Everything in the slot would see the variable --txtColor as red. display: contents; removes the wrapper from creating display issues (grids, etc).

<script>
	import { onMount } from 'svelte';
	let el;	
	onMount(() => {
		el.style.setProperty('--txtColor','red')
	});
	
</script>

<div bind:this={el} style="display: contents; ">
	<slot ></slot>
</div>

[josefaidt]

Hey @mdpotter55 :wave: thanks for raising this, and glad to hear you're enjoying the library! We can definitely add the variable styles to the wrapper component

\cc @dysfunc thoughts?

[mdpotter55]

It is only a point of discussion. The more I write things down, the better I see them. My method has its own issues to consider.

There is another way:

1. name a theme 'root' as a requirement (or it will default to the first).
2. apply the 'root' theme variables to ':root' to set the default.
3. All other themes are considered overlays and declared as classes.
4. When a user picks a theme, apply the overlay class to html or body.
5. This also allows an overlay to be used directly as a class instead of having to nest with a control.
6. This method can be accomplished with zero controls or a visually empty one. (perhaps even a preprocessor)
7. This method should also work much better with SSR & SEO and non-js (via svelteKit).