cant delete code from a custom.php file

Hi

I have this simple line of code in a custom.php file.
I want to remove the BG image ‘dots.png’
So I deleted the entire url and was left with just.. html body { background: #ffffff }
Then I hit the ‘Update File’ button in the WP editor, the entire url reappeared.
How can i remove this BG image?
Thanks

<?php header(‘Content-type: text/css’); ?>/* Custom Styles
……………………………………………………………………………………………………………………… */

html body { background: #ffffff url(‘../images/layout/small_dots.png’) repeat left top; }