SvelteKit routing not working ('/src/routes/about/+page.svelte' not mapped to '/about')

I'm very new to sveltkit. Just followed supabase-svelte app refered to this link. The supabased examples work good as it says.

Now I tried another things like routing reffering the official doc. It seems pretty easy and simple but not working for me.

This is my src structure

and the +page.svelte :

<h1>About this site</h1><p>TODO...</p><a href="/">Home</a>

And when I access to http://localhost:5173/about, it just seems main App.svelte.

This is my App.svelte just same as supabase-svelteapp.

<script lang="ts">    import { onMount } from 'svelte'    import { supabase } from './supabaseClient'    import type { AuthSession } from '@supabase/supabase-js'    import Account from './lib/Account.svelte'    import Auth from './lib/Auth.svelte'    let session: AuthSession | null    onMount(() => {      supabase.auth.getSession().then(({ data }) => {        session = data.session      })      supabase.auth.onAuthStateChange((_event, _session) => {        session = _session      })    })</script><div class="container" style="padding: 50px 0 100px 0">    {#if !session}<Auth />    {:else}<Account {session} />    {/if}</div>

I googled a lot, but coudln't find anything helpful..