What could be causing the issue with the size of the div containers in the PHP code provided?

The issue with the size of the div containers in the provided PHP code could be due to incorrect CSS styling or missing CSS properties that define the size of the div containers. To solve this issue, make sure to include CSS properties such as width and height in the style attribute of the div containers to specify their dimensions.

<?php
echo "<div style='width: 200px; height: 100px; background-color: red;'>Container 1</div>";
echo "<div style='width: 300px; height: 150px; background-color: blue;'>Container 2</div>";
?>