A text “d” suddenly started displaying across a website i am working on [closed]

After trying to increase my WordPress Memeory Limit in WP Config. I reloaded my site and started seeing the weird letter d displaying at the top of my website. All I pasted was this

define( 'WP_MEMORY_LIMIT', '256M' );

Here’s the site address here the site.

(Note: You might see it in maintenance mode, I just put up a page to show I am working on it, the website hasn’t been launched yet so no issues while it remains in maintenance mode)

I checked online and tried turning off error displays using the code below but still, it didn’t work. Please help me out. It displays across all pages of my website

ini_set('display_errors','Off');
ini_set('error_reporting', E_ALL );
define('WP_DEBUG', false);
define('WP_DEBUG_DISPLAY', false);