How to make table td taking up the whole width using css?

Question

I am making a site with tables mobile responsive. How do I make table td take up the whole full width(100%) using css?

<table>
    <tr>
        <td>Column One</td>
        <td>Column Two</td>
    </tr>
</table>

It is too hard to read information in two columns close to each other.

Answer 1

This will show the cells one below the other:

td {display:block;width:99.9%;clear:both}

or, as noted by @nux,

td {display:block; box-sizing:border-box; clear:both}

either should be enough, although microsoft browser won't oblige and you might need proprietary markup for those; then again if people plan to use a browser on their phone they wouldn't buy a microsoft phone, so the problem is minor.