Edit in JSFiddle

<ul>
    <li>foo</li><li>bar</li>
    <li>baz</li>
    <li>qux</li>
</ul>

ul {
    width: 130px;
    margin: 10px;
    padding: 5px;
    background-color: #CCC;
    font-size: 0;
    text-align: justify;
}

ul::after {
    content: '';
    display: inline-block;
    width: 100%;
}

li {
    display: inline-block;
    padding: 5px;
    background-color: black;
    color: white;
    font-family: sans-serif;
    font-size: 20px;
}