css就加入了一句display等于none，就操作不了滚动条了删除掉就可以滑动
display:none是元素被隐藏了。你滚动也没用
你是要这种效果吗
```html
<!DOCTYPE html>
<html>
<head>
<title>Combobox</title>
<meta charset="utf-8">
<style type="text/css">
*{
box-sizing:border-box;
}
input,select{
width: 200px;
}
#words{
display: none;
}
</style>
</head>
<body>
<input id="show" type="text" name=""> <br />
<select id="words">
<option>A</option>
<option>B</option>
<option>C</option>
<option>D</option>
<option>E</option>
<option>F</option>
<option>G</option>
</select>
<script type="text/javascript">
let show = document.getElementById('show');
let words = document.getElementById('words');
show.onclick = function(e){
words.style.display = 'block';
}
words.size = 3;
words.onchange = function(e){
var option = this.options[this.selectedIndex];
show.value = option.innerHTML;
words.style.display = 'none';
}
</script>
</body>
</html>
```
搬运自
https://blog.csdn.net/swl979623074/article/details/71438656/