Styling and Animation

Parts render without styles. The component demos use plain CSS, and the same state attributes and CSS variables work with Tailwind CSS or any other stylesheet.

Style a Part

Every part has a data-slot attribute. State adds attributes such as data-pressed and data-disabled:

<script lang="ts">
  import { Toggle } from "@ui-sdk/svelte/toggle"
</script>

<Toggle
  class="rounded-md border border-neutral-300 px-2.5 py-1.5 text-sm data-pressed:bg-neutral-100 data-disabled:opacity-50"
  >Bold</Toggle
>

Most state attributes are present or absent. Others have values, such as data-side="top". Each component's Styling section lists its attributes and CSS variables. Use those rather than generated IDs.

CSS Modules

Import a CSS Module and pass its class to the part. State selectors work the same way:

<script lang="ts">
  import { Toggle } from "@ui-sdk/svelte/toggle"
  import styles from "./toggle.module.css"
</script>

<Toggle class={styles.toggle}>Bold</Toggle>

.toggle {
  cursor: default;
  border: 1px solid var(--input, #e5e5e5);
  border-radius: 1.125rem;
  background: transparent;
  padding: 0.375rem 0.625rem;
  color: inherit;
  font: inherit;
  font-size: 0.875rem;
}

.toggle[data-pressed] {
  background: var(--muted, #f5f5f5);
}

.toggle[data-disabled] {
  opacity: 0.5;
}

.toggle:focus-visible {
  outline: 2px solid var(--ring, #a3a3a3);
  outline-offset: 2px;
}

You can also use Svelte's scoped styles. When a selector targets markup inside a component, use :global, such as :global([data-slot="toggle"]). CSS Modules avoid that scoping boundary.

Animate Opening and Closing

Popup content gets data-starting-style before it enters and data-ending-style while it exits. It stays mounted until the exit transition or animation finishes:

<script lang="ts">
  import {
    Popover,
    PopoverClose,
    PopoverContent,
    PopoverTitle,
    PopoverTrigger,
  } from "@ui-sdk/svelte/popover"
</script>

<Popover>
  <PopoverTrigger>Details</PopoverTrigger>
  <PopoverContent
    class="origin-(--transform-origin) transition-[opacity,scale] duration-150 data-starting-style:scale-96 data-starting-style:opacity-0 data-ending-style:scale-96 data-ending-style:opacity-0 motion-reduce:transition-none"
  >
    <PopoverTitle>Project Details</PopoverTitle>
    <p>Last updated today.</p>
    <PopoverClose>Done</PopoverClose>
  </PopoverContent>
</Popover>

Put exit styles on data-ending-style. data-closed describes the state but doesn't keep the element around for an exit.

Svelte Transitions

Svelte's own transitions work too. Put one on the element you render, with |global, since the block that adds and removes the element is inside the component. A popup stays visible above the page until its outro ends:

<script lang="ts">
  import {
    Popover,
    PopoverContent,
    PopoverTrigger,
  } from "@ui-sdk/svelte/popover"
  import { fade } from "svelte/transition"
</script>

<Popover>
  <PopoverTrigger>Details</PopoverTrigger>
  <PopoverContent aria-label="Project details">
    {#snippet render({ props })}
      <div {...props} transition:fade|global={{ duration: 150 }}>
        Last updated today.
      </div>
    {/snippet}
  </PopoverContent>
</Popover>

Popups provide --anchor-width and --available-height for sizing. Popups covers mounting and placement.

The ui-sdk Layer

A few behaviors need a little CSS, like keeping a closed popup hidden or dimming the page behind a sheet, so ui-sdk adds it to the page in a cascade layer named ui-sdk. Declare that layer at the top of your global stylesheet, like the app.css your root +layout.svelte imports, so your own styles win over it wherever the page puts them. With Tailwind, put it above @import "tailwindcss":

@layer ui-sdk;

A component's <style> block loads with the component, too late to come first, so keep the line in the global stylesheet.

ui-sdk adds this CSS once a component mounts, so HTML rendered on the server doesn't have it until the page hydrates. Closed content kept in the page, like a tooltip's, carries hidden, and a class that sets display shows it until then. Tailwind's base styles already hide hidden elements. With other CSS, add the same rule to your global stylesheet:

@layer ui-sdk {
  :where([data-slot][hidden]:not([hidden="until-found"])) {
    display: none !important;
  }
}

It leaves hidden="until-found" alone, so find in page can still open a closed panel.

Content Security Policy

A Content Security Policy without 'unsafe-inline' in style-src blocks the CSS ui-sdk adds. Give ui-sdk your policy's nonce with a meta tag in the page's <head>:

<meta property="csp-nonce" nonce="your-nonce" />

If your policy has no nonce for styles, add the tag without the nonce attribute. ui-sdk then adds its CSS as constructed style sheets, which no policy blocks. If your code replaces document.adoptedStyleSheets, ui-sdk adds its sheets back the next time a component mounts.

In SvelteKit, put the tag without a nonce in src/app.html. It works with any kit.csp mode, on prerendered pages too, as long as @layer ui-sdk; comes first in your global stylesheet:

<meta property="csp-nonce" />

SvelteKit's nonce="%sveltekit.nonce%" works only when style-src carries that nonce, and SvelteKit adds it there only for CSS it inlines itself, which kit.inlineStyleThreshold turns on. The placeholder also stops a page from being prerendered.

With Vite alone, set html.cspNonce in your Vite config to a placeholder, and Vite writes the tag for you. Your server replaces the placeholder with a new nonce on each request.

Keep Svelte's default css: "external" under a strict policy, since css: "injected" adds each component's styles as a <style> without a nonce.

Pages rendered on the server also carry a few style attributes, like the one that hides a select's native input, so the policy needs style-src-attr 'unsafe-inline' too.