JSFiddle - React, Tailwind, and code Playground

HTML

<div id="mainCont">
    <div id="stretchParent">
        This div should make its parent bigger
    </div>
    <div id="fillParent">
        <span>TagItem</span>
        <span>TagItem</span>
        <span>TagItem</span>
        <span>TagItem</span>
        <span>TagItem</span>
        <span>TagItem</span>
    </div>
</div>
<br/><br/><br/><br/>
<div id="mainCont">
    <div id="stretchParent">
        This div should make its parent bigger
    </div>
    <div id="fillParent">
        <span>TagItem</span>
        <span>TagItem</span>
        <span>TagItem</span>
        
        <br/>
        
        <span>TagItem</span>
        <span>TagItem</span>
        <span>TagItem</span>
    </div>
</div>

CSS

#stretchParent
{
    background-color:gray
}
#mainCont
{
    display:inline-block;
}
#fillParent
{
    background-color:green;
}
#fillParent span
{
    border :1px solid black;
    margin:.2em;
    background-color:white;
}