finish custom class and improved options overhaul

src/lib/Checkbox.svelte

@@ -6,12 +6,14 @@
 	import type { Snippet } from 'svelte';
 	import { validate } from '@svelte-toolkit/validate';
 	import { generateIdentifier } from './util.js';
+	import type { ClassValue } from 'svelte/elements';
 
 	interface Props {
 		name?: string;
 		required?: boolean;
 		value?: CheckboxState;
 		color?: 'default' | 'contrast';
+		class?: ClassValue | null | undefined;
 		children?: Snippet;
 		onchange: (value: CheckboxState) => void;
 	}
@@ -21,6 +23,7 @@
 		required = false,
 		value = $bindable(false),
 		color = 'contrast',
+		class: classValue,
 		children,
 		onchange
 	}: Props = $props();
@@ -30,7 +33,7 @@
 	let valid = $state(true);
 </script>
 
-<div class="flex items-center">
+<div class={['flex items-center', classValue]}>
 	<input
 		type="hidden"
 		{name}