combobox: improve icon padding behaviour

Tween the value and make it more consistent with the underlying
StyledRawInput type.

src/lib/Combobox.svelte

@@ -50,6 +50,8 @@
 	import { matchSorter } from 'match-sorter';
 	import Spinner from './Spinner.svelte';
 	import type { KeyOption } from 'match-sorter';
+	import { Tween } from 'svelte/motion';
+	import { cubicOut } from 'svelte/easing';
 
 	interface Props {
 		/**
@@ -147,7 +149,6 @@
 		 */
 		searchKeys?: ('value' | 'label' | 'preview' | 'infotext')[];
 
-		// TODO: implement searchKeys above.
 		/** Additional classes applied to the persistent div container */
 		class?: ClassValue | null | undefined;
 		/** Optional action applied to the main input */
@@ -216,7 +217,6 @@
 	let searchValue = $state('');
 	let pickerPosition = $state<'top' | 'bottom'>('bottom');
 	let searching = $state(false);
-	let iconWidth = $state<number | undefined>(undefined);
 
 	let searchInput = $state<HTMLInputElement | null>(null);
 	let searchContainer = $state<HTMLDivElement | null>(null);
@@ -264,6 +264,29 @@
 	/** validation options build from props */
 	const validateOpts: ValidatorOptions = $derived({ required });
 
+	/** calculates padding for the input based on icon visibility and size */
+	const calculatePadding = () => {
+		const gap = 5; // gap between icon and text
+		// base padding when no icon is visible, see StyledRawInput padding
+		const basePadding = compact ? 12 : 18;
+		// if icon is visible, padding is icon width + gap + base padding,
+		// otherwise it's just base padding
+		return iconVisible ? iconWidth + gap + basePadding : basePadding;
+	};
+	let iconWidth = $state<number>(0);
+	/** tweens main input padding */
+	const inputPadding = new Tween(calculatePadding(), {
+		duration: 150,
+		easing: cubicOut
+	});
+	$effect(() => {
+		if (iconWidth >= 0) {
+			untrack(() => {
+				inputPadding.target = calculatePadding();
+			});
+		}
+	});
+
 	/*** HELPER FUNCTIONS ***/
 
 	/** returns the index of the highlighted item in filteredItems */
@@ -637,8 +660,8 @@
 		{#if iconVisible}
 			<div
 				class={[
-					(iconWidth === undefined || iconWidth === 0) && 'opacity-0',
+					'pointer-events-none absolute top-1/2 left-3.5 -translate-y-1/2 transform select-none',
-					'pointer-events-none absolute top-1/2 left-3.5 -translate-y-1/2 transform select-none'
+					iconWidth === 0 && 'opacity-0'
 				]}
 				transition:scale
 				bind:clientWidth={iconWidth}
@@ -663,7 +686,7 @@
 
 		<!-- Combobox input box -->
 		<StyledRawInput
-			style={iconWidth && iconVisible ? `padding-left: ${iconWidth + 14 + 10}px` : undefined}
+			style={`padding-left: ${inputPadding.current}px`}
 			class={[caret && 'pr-9', !valid && 'border-red-500!']}
 			{compact}
 			type="text"