1.使用Modal下的API getContainer 来获取 指定 Modal 挂载的 HTML 节点，同时css中使用深度选择器:deep

2.完整代码

<template>
 <div class="modal-wrapper" ref="modal">
            <a-modal
              v-model:visible="addRuleModal"
              title="新建互动"
              centered
              okText="保存"
              cancelText="取消"
              :getContainer="() => $refs.modal"
              @ok="onFinish(state.formState, state.dataRule)"
              @cancel="resetForm"
            >
            <div class="content">
<span>
Hello World!
</span>
</div>
            </a-modal>
          </div>
</template>
<style lang="less" scoped>
  :deep(.modal-wrapper) {
      .content{
        color: #1f1f1f;
      }
    }
</style>