Unused CSS selector "*"

[bienoubien-studio]

Describe the bug

Using global in svelte style tag throw a warning : Unused CSS selector "*" but no rules like these are defined.
Using Svelte 5, I don't know if it could be related.

The component :

<script lang="ts">
	import { Label as LabelPrimitive } from 'bits-ui';

	let {
		ref = $bindable(null),
		class: className,
		...restProps
	}: LabelPrimitive.RootProps = $props();
</script>

<LabelPrimitive.Root bind:ref class="cms-label {className}" {...restProps} />

<style lang="postcss">
	:global(.cms-label) {
		display: inline-block;
		font-size: var(--cms-text-sm);
	}
	:global(.cms-label ~ :disabled) {
		opacity: 0.7;
		cursor: not-allowed;
	}
</style>

Same error with a global attribute on the style tag instead of :global() with svelte-preprocess

Reproduction URL

https://github.com/bienoubien-studio/svelte-preprocess-unused-css-issue

Reproduction

git clone https://github.com/bienoubien-studio/svelte-preprocess-unused-css-issue.git
cd svelte-preprocess-unused-css-issue
pnpm install
pnpm dev

Then visit http://localhost:5173

Logs

[vite-plugin-svelte] src/lib/label/label.svelte:22:1 Unused CSS selector "*"

System Info

System:
    OS: macOS 15.0
    CPU: (8) arm64 Apple M2
    Memory: 70.13 MB / 8.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 22.8.0 - ~/.nvm/versions/node/v22.8.0/bin/node
    npm: 10.8.2 - ~/.nvm/versions/node/v22.8.0/bin/npm
    pnpm: 9.1.1 - /opt/homebrew/bin/pnpm
    bun: 1.1.17 - /opt/homebrew/bin/bun
  Browsers:
    Brave Browser: 129.1.70.117
    Chrome: 124.0.6367.208
    Safari: 18.0
  npmPackages:
    @sveltejs/adapter-auto: ^3.0.0 => 3.2.5 
    @sveltejs/kit: ^2.0.0 => 2.6.1 
    @sveltejs/vite-plugin-svelte: ^4.0.0-next.6 => 4.0.0-next.7 
    svelte: ^5.0.0-next.1 => 5.0.0-next.260 
    vite: ^5.0.3 => 5.4.8

[bienoubien-studio]

Looks like it's may be related to svelte 5 : sveltejs/svelte#13399

[dominikg]

see sveltejs/svelte#13399 (comment)

[forna]

see sveltejs/svelte#13399 (comment)

You should not be using svelte scoped style blocks to add global css.

https://github.com/sveltejs/vite-plugin-svelte/blob/main/docs/faq.md#where-should-i-put-my-global-styles

Sometimes it is needed, check this example.
I defined my own spinner component that imports the svelte-loading-spinners library.
I prefer to customize the CSS for each component within the component itself, but since the CSS ids and classes are defined in the svelte-loading-spinners, then I must use global.

<script>
    import {Circle2} from "svelte-loading-spinners"

    // Props
    let {loadSpinner}  = $props()
</script>

{#if loadSpinner}
    <Circle2 size=60 colorOuter="#8A2BE2" colorCenter="#46B4FD" 
    colorInner="#FFD700" durationOuter="2s" durationCenter="1.5s" durationInner="1s" />
{/if}

<style>
    :global { 
        .circle, .wrapper {    /* These are defined in svelte-loading-spinners */
            position: fixed !important; 
            top: 50% !important;
            left: 50% !important;
            margin-top: var(--margin-top) !important; 
            margin-left: var(--margin-left) !important; 
            display: flex !important;
            justify-content: center !important;
            align-items: center !important;
            z-index: 10000 !important; 
        }
    }
</style>

But with this code I get the warning:
[vite-plugin-svelte] src/lib/components/component/Spinner.svelte:40:1 Unused CSS selector "*"

[bienoubien-studio]

see sveltejs/svelte#13399 (comment)

see https://svelte.dev/docs/svelte/global-styles

[dominikg]

see sveltejs/svelte#13399 (comment)

see https://svelte.dev/docs/svelte/global-styles

svelte can be used outside of vite where you might not have other means to define global styles.
But if you use vite and vite-plugin-svelte it is strongly discouraged to do this as vite offers vastly superior ways to define and load global styles.

The warning for the * selector is a bit of an unfortunate sideeffect that only happens with components that don't have targetable nodes in their own template - and only during development.

You can easily silence this warning using the new svelte5 warningFilter option in svelte.config.js

	compilerOptions: {
		warningFilter(w){
			return w.message !== 'Unused CSS selector "*"'
		}
	},

or the more generic onwarn

	onwarn(w, warn){
		if(w.message !== 'Unused CSS selector "*"') {
			warn(w)
		}
	}

[bienoubien-studio]

svelte can be used outside of vite where you might not have other means to define global styles.

Ok, but i don't really think it's an argument as npx sv create myapp or the previous npm create svelte@latest myapp setup a vite project so 99% of the time people will use vite and get warnings for something they didn't do.

Ok for the compiler option, but let's say I am building a package with some components dependencies I need to style , then people using it will have multiple warnings for something they don't know about.

I feel like if I am following at 100% documentation I should not have warnings.

[dominikg]

esp. libraries should always use scoped style or ship global styles as external css file.

users projects won't see a warning for libraries with this issue as they don't get the * selector injected.