JSFiddle - React, Tailwind, and code Playground

HTML

These 4 items should fill the width:<br/>
<ul id="ul1">
    <li>item</li>
    <li>item</li>
    <li>item</li>
    <li>item</li>
</ul>
These 7 items should fill the width:<br/>
<ul id="ul2">
    <li>item</li>
    <li>item</li>
    <li>item</li>
    <li>item</li>
    <li>item</li>
    <li>item</li>
    <li>item</li>
</ul>
And so on and so forth...

CSS

ul {
    border:1px dotted black;
    padding: 0;
    display:table;
    width:100%;
    box-sizing:border-box;
    -moz-box-sizing:border-box;
    -webkit-box-sizing:border-box;
}
li {
    background-color: red;
    display:table-cell;
}
li:nth-child(2n) {
    background-color: #0F0;
}