JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="flex-container">
    <li class="flex-item">1</li>
    <li class="flex-item">2</li>
    <li class="flex-item">3</li>
    <li class="flex-item">4</li>
    <li class="flex-item">5</li>
    <li class="flex-item">6</li>
</ul>

CSS

.flex-container {
    position: fixed;
    height: 90%;

    padding: 0;
    margin: 0;
    list-style: none;
    border: 6px solid green;

    display: -webkit-box;
    display: -moz-box;
    display: -ms-flexbox;
    display: -webkit-flex;
    display: flex;

    -webkit-flex-flow: column wrap;
    justify-content: flex-start
    align-content: flex-start;
    align-items: flex-start
}


/** Just to show the elements */
body {
    margin: 0;
    padding: 0;
}
.flex-item {
    background: tomato;
    padding: 5px;
    width: 100px;
    height: 100px;
    margin-top: 10px;

    line-height: 150px;
    color: white;
    font-weight: bold;
    font-size: 3em;
    text-align: center;
}