这是不可能的。您只能实现自己的选择框，但这对于可用性是不利的。

This is not possible. You can only implement your own select-box, but this is bad for usability.

另一种方法是以编程方式更改选择框的大小属性，但这不是真的你想要的。

another approach is to programmatically change the size-attribute of the select-box, but this is not really what you wanted.

我建议你想想你为什么需要这个，如果会有更好的软件模式？

I suggest to think of why you need this and if there would be a nicer software-pattern?