docs(BackToTop): update to use VFab

packages/docs/src/components/app/BackToTop.vue

@@ -1,25 +1,14 @@
 <template>
-  <v-layout-item
-    class="text-end pointer-events-none"
-    position="bottom"
-    size="88"
-    model-value
+  <v-fab
+    v-model="model"
+    color="primary"
+    elevation="8"
+    icon="mdi-chevron-up"
+    size="large"
+    app
     v-scroll="onScroll"
-  >
-    <div class="ma-4">
-      <v-fab-transition>
-        <v-btn
-          v-show="model"
-          class="mt-auto pointer-events-initial"
-          color="primary"
-          elevation="8"
-          icon="mdi-chevron-up"
-          size="large"
-          @click="goTo(0)"
-        />
-      </v-fab-transition>
-    </div>
-  </v-layout-item>
+    @click="goTo(0)"
+  />
 </template>
 
 <script setup>
@@ -31,13 +20,3 @@
     model.value = window.scrollY > 200
   }
 </script>
-
-<style scoped>
-  .pointer-events-none {
-    pointer-events: none;
-  }
-
-  .pointer-events-initial {
-    pointer-events: initial;
-  }
-</style>