elementUI dialog 对话框层级问题

 解决办法，需给el-dialog 加上 append-to-body

代码如下：

<el-dialog
      title="提示"
      append-to-body
      style="z-index:3000"
      :visible.sync="infoDialog"
      width="30%"
      :before-close="handleClose">
      <span>这是一段信息</span>
      <span slot="footer" class="dialog-footer">
        <el-button @click="infoDialog = false">取 消</el-button>
        <el-button type="primary" @click="infoDialog = false">确 定</el-button>
      </span>
    </el-dialog>