added PageTop component, markdown styles, white background on logo svg, and documentation comments

error.vue

@@ -0,0 +1,21 @@
+<script setup lang="ts">
+import type { NuxtError } from "#app";
+
+const props = defineProps({
+    error: Object as () => NuxtError,
+});
+
+definePageMeta({
+    layout: "default",
+});
+</script>
+
+<template>
+    <NuxtLayout>
+        <div>
+            <h1>{{ error?.statusCode }}</h1>
+            <p>{{ error?.message }}</p>
+            <NuxtLink to="/">戻る</NuxtLink>
+        </div>
+    </NuxtLayout>
+</template>