JSFiddle - React, Tailwind, and code Playground

HTML

<div id="outerWrapper">
    <ul id="innerWrapper">
        <li class="child">I'm #01</li>
        <li class="child">I'm #02</li>
        <li class="child">I'm #03</li>
        <li class="child">I'm #04</li>
        <li class="child">I'm #05</li>
    </ul>
</div>

CSS

#outerWrapper {
    height: 300px;
    background-color: lightgreen;
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    align-items: flex-end;
}

ul {
    padding: 0;
    margin: 0;
    display: flex;
    align-items: center;
    flex-wrap: wrap;
    flex-direction: column;
    height: 100%;                           /* NEW */
}

li {
    list-style-type: none;
    width: 100px;
    height: 100px;
    background-color: lightblue;
    border: 1px solid;
}

li:nth-child(odd) { margin-top: auto; }      /* NEW */

ul::after {
    content: "";                              /* NEW */
    width: 100px;                             /* NEW */
    height: 100px;                            /* NEW */
    border: 1px solid;                        /* NEW */
    visibility: hidden;                       /* NEW */
}