try this

Author: Rich-Harris

apps/svelte.dev/src/routes/tutorial/[slug]/filetree/Item.svelte

@@ -42,7 +42,8 @@
 <!-- svelte-ignore a11y-no-noninteractive-element-interactions -->
 <li
 	aria-current={selected ? 'true' : undefined}
-	style="--depth: {depth}; --icon: url({icon});"
+	style:--depth={depth}
+	style:--icon="url(&quot;{icon}&quot;)"
 	on:keydown
 >
 	{#if renaming}