HTML/CSS table: how to make zero border for all the cells?

Question

I would like to create an HTML table whose cells are filled with images (say this red square), and I do not want any padding/border/margin between cells.

My HTML is like below:

<table>
  <tr>  <td><img src="red.png"></td> <td><img src="red.png"></td>  </tr>
  <tr>  <td><img src="red.png"></td> <td><img src="red.png"></td>  </tr>
  <tr>  <td><img src="red.png"></td> <td><img src="red.png"></td>  </tr>
</table>

And my CSS code is

table {
  margin: 0px;
  border: 0px;
  padding: 0px;
  border-spacing: 0px;
}
tr {
  margin: 0px;
  border: 0px;
  padding: 0px;
}
td {
  margin: 0px;
  border: 0px;
  padding: 0px;
}

However, it only collapse the horizontal border, but not vertical ones, and the result rendering is as below, and I expect a large 3x2 red square.

Thanks in advance for your help!