feat: 调整 App.vue 中组件的宽度设置，优化布局

src/all-custom-primevue/all-custom-primevue.vue

@@ -1,10 +1,10 @@
 <template>
+  <Fieldset
+    legend="Form 1"
+    pt:content:class="flex justify-center"
+  >
 
-  <form @submit.prevent="onFormSubmit">
-    <Fieldset
-      legend="Form 1"
-      pt:content:class="flex flex-col gap-4 w-full sm:w-56"
-    >
+    <form @submit.prevent="onFormSubmit">
 
       <div class="flex flex-col gap-1">
         <label for="username">Username</label>
@@ -62,8 +62,8 @@
         severity="secondary"
         label="Submit"
       />
-    </Fieldset>
-  </form>
+    </form>
+  </Fieldset>
 </template>
 
 <script setup lang="ts">