实现效果：

点击切换箭头方向

实现代码

    <div
      class="modelPart"
      @click="showClick"
    >
      <div class="modelPart_left">
        <img
          :src=aidefalutIcon
          class="sNodeIcon"
        >
        <div>{{ selectModel }}</div>
        <div class="chatText">CHAT</div>
      </div>
      <span :class="dropdown==true?'expand':'down'"
           class="arrow"></span>
    </div>

<script setup>
     import { useI18n } from 'vue-i18n';
     const { t } = useI18n();
     import { onMounted, ref, watch } from 'vue'
     const dropdown = ref(false)
     // 点击事件
     function showClick () {
         dropdown.value = !dropdown.value
     }
</script>

  .arrow {
    display: inline-block;
    width: 7px;
    height: 7px;
    margin-top: -3px;
    margin-left: 9px;
    border-top: 2px solid #ffffff;
    border-left: 2px solid #ffffff;
   
  }
  .down{
   transform: rotate(225deg);
   transform-origin: center;
   transition: all 0.3s;
}
  .expand {
    transform: translate(0, 2px) rotate(45deg);
    transform-origin: center;
    transition: all 0.3s;
 }