JSFiddle - React, Tailwind, and code Playground

HTML

<table style="width:100%;">
    <tr>
        <td style="border:1px solid black;width:100px;height:10px;"></td>
        <td style="border:1px solid black;height:10px;"></td>
    </tr>
</table>
<br /><br />

<div class="lineContainer">
    <div class="left"></div>
    <div class="right"></div>
</div>

CSS

.lineContainer {
    display:table;
    border-collapse:collapse;
    width:100%;
}
.lineContainer div {
    display:table-cell;
    border:1px solid black;
    height:10px;
}
.left {
    width:100px;
}