为什么显示出来没有样式啊
@vue/cli 4.5.13

<template>
  <a-layout>
    <a-layout-header class="header">
      <div class="logo" />
      <a-menu
              theme="dark"
              mode="horizontal"
              v-model:selectedKeys="selectedKeys1"
              :style="{ lineHeight: '64px' }"
      >
        <a-menu-item key="1">nav 1</a-menu-item>
        <a-menu-item key="2">nav 2</a-menu-item>
        <a-menu-item key="3">nav 3</a-menu-item>
      </a-menu>
    </a-layout-header>
    <a-layout>
      <a-layout-sider width="200" style="background: #fff">
        <a-menu
                mode="inline"
                v-model:selectedKeys="selectedKeys2"
                v-model:openKeys="openKeys"
                :style="{ height: '100%', borderRight: 0 }"
        >
          <a-sub-menu key="sub1">
            <template #title>
              <span>
                <user-outlined />
                subnav 1
              </span>
            </template>
            <a-menu-item key="1">option1</a-menu-item>
            <a-menu-item key="2">option2</a-menu-item>
            <a-menu-item key="3">option3</a-menu-item>
            <a-menu-item key="4">option4</a-menu-item>
          </a-sub-menu>
          <a-sub-menu key="sub2">
            <template #title>
              <span>
                <laptop-outlined />
                subnav 2
              </span>
            </template>
            <a-menu-item key="5">option5</a-menu-item>
            <a-menu-item key="6">option6</a-menu-item>
            <a-menu-item key="7">option7</a-menu-item>
            <a-menu-item key="8">option8</a-menu-item>
          </a-sub-menu>
          <a-sub-menu key="sub3">
            <template #title>
              <span>
                <notification-outlined />
                subnav 3
              </span>
            </template>
            <a-menu-item key="9">option9</a-menu-item>
            <a-menu-item key="10">option10</a-menu-item>
            <a-menu-item key="11">option11</a-menu-item>
            <a-menu-item key="12">option12</a-menu-item>
          </a-sub-menu>
        </a-menu>
      </a-layout-sider>
      <a-layout style="padding: 0 24px 24px">
        <a-breadcrumb style="margin: 16px 0">
          <a-breadcrumb-item>Home</a-breadcrumb-item>
          <a-breadcrumb-item>List</a-breadcrumb-item>
          <a-breadcrumb-item>App</a-breadcrumb-item>
        </a-breadcrumb>
        <a-layout-content
                :style="{ background: '#fff', padding: '24px', margin: 0, minHeight: '280px' }"
        >
          Content
        </a-layout-content>
      </a-layout>
    </a-layout>
  </a-layout>
</template>

<style>
  #components-layout-demo-top-side-2 .logo {
    float: left;
    width: 120px;
    height: 31px;
    margin: 16px 24px 16px 0;
    background: rgba(255, 255, 255, 0.3);
  }

  .ant-row-rtl #components-layout-demo-top-side-2 .logo {
    float: right;
    margin: 16px 0 16px 24px;
  }

  .site-layout-background {
    background: #fff;
  }

#nav a {
  font-weight: bold;
  color: #2c3e50;
}

#nav a.router-link-exact-active {
  color: #42b983;
}
</style>