hi,
i have question is there any code that adjustmy custom backgound to be fit in the mobile and tablets (responsive) ?
It should be responsive by default so I am not really sure what you are trying to achieve. It would help if you could post your website URL because each setup is different and there’s no one size fit all solution.
For more specific responsive optimization you can use media queries (@media) if you want to make it different for each device.