Backport DataList, DataListItem and other improvements from svelte5 to main

[Copilot]

Backports components and improvements from the svelte5 branch to main (svelte3/4), converting Svelte 5 syntax ($props, $derived, $state, snippets) to Svelte 3/4 equivalents (export let, $:, slots).

New components

• DataList — Container <ul> with CSS variable theming for icon sizes, action layouts, borders, selection colors, and container-query responsive stacking
• DataListItem — Grid-based <li> row with start/end named slots, interactive and selectable modes, keyboard activation, and nested control click isolation
• Form / Fieldset — Styled wrappers integrating with FormProvider for cascading form layout defaults
• FormProvider — Svelte store-based context provider for form defaults (layout, fullWidth, globalInputStyles, multiline)
• Option — Rich HTML <option> wrapper using data-html attribute for custom dropdown rendering in Select
• types.ts — CSS variable prop interfaces (BaseStyleProps, ContainerStyleProps, etc.)

Enhanced existing components

• FormItem — Layout modes (side/above/below), multiline prop, context defaults from FormProvider, grid CSS for above/below layouts
• Select — Reads data-html from options, change event bubbles, focus styles on dropdown buttons

SCSS / theme fixes

• _color.scss — Re-defines --fg/--bg so nested components inherit correctly
• _box.scss — New box-size-props mixin
• _typography.scss — Heading colors use explicit --heading-fg/--heading-bg fallbacks
• _affordances.scss — Hover brightness 1.4 → 1.05
• Dark theme secondary colors fixed for dark backgrounds

Usage

<DataList maxWidth="800px" iconSize="3rem" iconBorderRadius="50%">
  <DataListItem selectable bind:checked={selected}>
    <img slot="start" src="avatar.jpg" alt="" />
    <h4>Title</h4>
    <p>Description text</p>
    <span slot="end">
      <Button>Action</Button>
    </span>
  </DataListItem>
</DataList>

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[thinkle-iacs]

Hey -- I fixed a package issue in this branch for you (existing problem).

Bigger issue: you didn't backport DataList and DataListItem. Please add those!

[Copilot]

Pull request overview

Backports UI components and styling improvements from the svelte5 branch to the Svelte 3/4 codepath, adding form-related primitives and updating theming/CSS variable behavior.

Changes:

• Add new layout/components: FormProvider, Form, Fieldset, and control Option (for rich select options), plus exported TS style-prop interfaces.
• Enhance FormItem with layout modes (side|above|below), context-driven defaults, and grid-based layout styles.
• Update theming/styling utilities and SCSS (dark theme secondary colors, affordances vars, typography heading vars, color/box mixins) and improve Select rich option rendering + bubbled change events.

Reviewed changes

Copilot reviewed 15 out of 16 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
src/lib/vars/themes/dark.css	Adjust dark theme secondary fg/bg variables for better contrast.
src/lib/vars/affordances.css	Add scrollbar track background custom property.
src/lib/util.ts	Broaden injectVars prop typing.
src/lib/types.ts	Add exported TS interfaces for common CSS-variable props.
src/lib/sass/_typography.scss	Update heading color/background variable fallback behavior.
src/lib/sass/_color.scss	Modify color-props mixin to re-define --fg/--bg for nesting.
src/lib/sass/_box.scss	Add box-size-props mixin for width/height/min/max controls.
src/lib/sass/_affordances.scss	Reduce default hover brightness.
src/lib/layout/FormProvider.svelte	New context provider for form defaults (layout/fullWidth/etc.).
src/lib/layout/FormItem.svelte	Add context defaults + new layout modes and grid CSS.
src/lib/layout/Form.svelte	New styled <form> wrapper with FormProvider integration.
src/lib/layout/Fieldset.svelte	New styled <fieldset> wrapper with legend slot and FormProvider integration.
src/lib/index.ts	Export new components and style-prop types.
src/lib/controls/Select.svelte	Support rich option HTML via data-html, bubble change events, add focus styles.
src/lib/controls/Option.svelte	New helper component to populate <option data-html> from slotted markup.
package-lock.json	Update lockfile (version bump and Svelte version alignment).

Comments suppressed due to low confidence (1)

src/lib/util.ts:13

• Changing injectVars to accept { [key: string]: any } hides type errors and can generate invalid CSS when non-string values are passed (e.g. booleans become true/false, objects become [object Object]). Consider narrowing this to a safe union (string/number/null/undefined) and/or coercing/ignoring unsupported types before interpolating into the style string to avoid producing invalid custom property values.

export function injectVars(
  props: { [key: string]: any },
  prefix: string,
  varList: string[]
) {
  let cssVars = "";
  varList.forEach((v) => {
    if (props[v]) {
      const cssVarName = toKebabCase(v);
      cssVars += `--${prefix}-${cssVarName}: ${props[v]};`;
    }

---

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[Copilot]

Option currently renders both an <option> and a hidden <div>. When used inside a native <select>, the extra <div> is invalid HTML (a <select>'s content model only allows <option>, <optgroup>, and optionally <script>/<template>), and browsers may move/drop the element, breaking measurement/extraction and potentially the select itself. Consider using a <template> element for the hidden markup (allowed inside <select>) or extracting the HTML in another way that doesn't introduce non-option children.

[Copilot]

color-props now assigns --fg/--bg using fn.var-no-fallbacks(--fg/--bg, ...), which expands to a value that ultimately references var(--fg, unset) / var(--bg, unset). Setting a custom property in terms of itself creates a cyclic dependency and makes the variable invalid at computed-value time, which can break downstream var(--fg)/var(--bg) usage. To achieve inheritance for nested components, set --fg/--bg from prefixed variables without referencing the same property name (e.g. fall back to inherit/unset, or use a helper that doesn't include the base --fg/--bg in the chain).

Suggested change

	--fg: #{fn.var-no-fallbacks(--fg, $prefixes...)};
	--bg: #{fn.var-no-fallbacks(--bg, $prefixes...)};
	--fg: #{fn.vars(fg, $prefixes...)};
	--bg: #{fn.vars(bg, $prefixes...)};

[Copilot]

border is typed as string | boolean | undefined and then fed into injectVars as a CSS custom property. If a consumer passes border={true}, injectVars will emit --form-border: true; which is not a valid CSS border value and can cause border: var(--form-border, ...) to compute unexpectedly. Prefer making border a string CSS value only, or use a separate boolean like bordered/showBorder to switch to a default border style.

[Copilot]

border is typed as string | boolean | undefined and then passed through injectVars. Passing border={true} would emit a --fieldset-border: true; custom property, which is not a valid border value and may lead to unexpected computed styles. Consider restricting border to a string CSS value, or splitting the API into a boolean flag for default border vs. a string override.

Suggested change

	export let border: string | boolean | undefined = undefined;
	export let border: string | undefined = undefined;

[Copilot]

FormProvider reads the parent defaults store via get(parentStore) inside a reactive block, but get() does not establish a reactive subscription. As a result, updates to a parent FormProvider's store won't propagate to this provider (nested providers won't update when parent values change). Use a store subscription (e.g. $parentStore in a $: statement) or derived() to recompute when the parent store updates, and then store.set(...) from those reactive values.

[Copilot]

contextDefaults is computed with get(contextStore), which won't update when the context store emits new values. That means changing layout/fullWidth/globalInputStyles/multiline on the surrounding FormProvider after initial render won't update this FormItem. Subscribe reactively to the store (e.g. use $contextStore in a $: block) instead of calling get() inside a reactive statement.

[Copilot]

Here richHtml is populated from optionEl.dataset.html ?? optionEl.innerHTML and then stored in options[idx].html, which is later rendered via {@html ...} in this component. If any option label or data-html attribute is derived from attacker-controlled data (for example, user input or external API responses), this flow will turn what Svelte normally treats as safe text into executable HTML/JS in the custom dropdown, enabling DOM XSS. To mitigate this, avoid feeding untrusted values into dataset.html/option contents for this component or introduce a sanitization/whitelisting step before assigning to richHtml and using it with @html.

[Copilot]

Here htmlContent is taken from template.innerHTML and written into the data-html attribute of the <option>, which is later consumed by Select.svelte and rendered with {@html}. This means that slot content containing </> (including attacker-controlled strings that Svelte would normally escape as text) can be turned back into live HTML/JS in the custom dropdown, enabling DOM XSS if an attacker controls the option label. To mitigate this, avoid feeding untrusted slot content into this component or ensure the extracted HTML is sanitized/whitelisted before exposing it via data-html for use with {@html}.