JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
<ul>
    <li>1</li>
    <li>2</li>
    <li>3</li>
    <li>4</li>
    <li>5</li>
    <li>6</li>
</ul>
</div>

<p style="text-align: center">The parent container is always centered. The flex items are aligned left.</p>

CSS

#container {
    display: flex;
    justify-content: center;
}

ul {
    display: flex;
    flex-direction: row;
    flex-wrap: wrap;
    justify-content: flex-start;
    margin: 0;
    padding: 0;
    border: 5px solid green;
    Width: 90%;
}

li {
    list-style-type: none;
    border: 1px solid gray;
    margin: 15px;
    padding: 5px;
    width: 200px;
}