JSFiddle - React, Tailwind, and code Playground

HTML

<select name="number-of-stuffs">
    <option value="1">1</option>
    <option value="2">2</option>
    <option value="3">3</option>
</select>
<div class="stuff-1">
    <input type="text" name="stuff-1-detail" />
    <input type="text" name="stuff-1-detail2"/>
</div>
<div class="stuff-2" style="display:none"> 
    <input type="text" name="stuff-2-detail" />
    <input type="text" name="stuff-2-detail2" />
</div>
<div class="stuff-3" style="display:none">
    <input type="text" name="stuff-3-detail" />
    <input type="text" name="stuff-4-detail2" />
</div>

CSS

select[name="number-of-stuffs"] option[value="2"]:checked - div.stuff-2, 
select[name='number-of-stuffs'] option[value="3"]:checked - div.stuff-2.
select[name='number-of-stuffs'] option[value="3"]:checked - div.stuff-3
{
    display: block;
    background: green;
}