JSFiddle - React, Tailwind, and code Playground

HTML

<table class="tblLayout" border="1">
    <tr>
        <td colspan="2" height="96px">
            <h1>Header</h1>
        </td>
    </tr>
    <tr>
        <td width="33%">
            <h1>Left</h1>
        </td>
        <td>
            <h1>Content</h1>
        </td>
    </tr>
</table>

CSS

.tblLayout {
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    width: 100%;
    height: 100%;
}