JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="li_inline">
    <li>
        <ul class="li_block">
            <li>Stuff</li>
            <li>Stuff under stuff</li>
        </ul>
    </li>
    <li>
        <ul class="li_block">
            <li>Stuff</li>
            <li>Stuff under stuff</li>
        </ul>
    </li>
    <li>
        <ul class="li_block">
            <li>Stuff</li>
            <li>Stuff under stuff</li>
        </ul>
    </li>
    <li>
        <ul class="li_block">
            <li>Stuff</li>
            <li>Stuff under stuff</li>
        </ul>
    </li>
    <li>
        <ul class="li_block">
            <li>Stuff</li>
            <li>Stuff under stuff</li>
        </ul>
    </li>
    <li>
        <ul class="li_block">
            <li>Stuff</li>
            <li>Stuff under stuff</li>
        </ul>
    </li>    
</ul>

CSS

ul { 
    border:1px solid #000;
    margin:2px;
}

.li_inline > li { display:inline; }

.li_block {
    display:inline-block;
}