vue element-ui的对话框dialog没有height怎么解决？

<el-dialog
  ref="elDialog"
  title="提示"
  :visible.sync="dialogVisible"
  width="30%"
  :before-close="handleClose">
  <span>这是一段信息</span>
  <span slot="footer" class="dialog-footer">
    <el-button @click="dialogVisible = false">取 消</el-button>
    <el-button type="primary" @click="dialogVisible = false">确 定</el-button>
  </span>
</el-dialog>


this.$refs.elDialog[0].$el.firstChild.style.height = ‘90%‘;