Thank you for reaching out,

Instead of using custom CSS, you can set a standard background for your site through the Customizer settings. Please navigate to WP Dashboard > Appearance > Customizer > Site Style & Settings > Site Layout; Please follow the steps explained in this link: https://docs.oceanwp.org/article/898-customizer-site-style-settings#Site-Layout-kC1LX

I hope it helps,
Best Regards

You’re welcome. I’m glad we could help.

Yes, and that seems it’s a cache issue, if you have any cache plugin or server cache(CDN / Browser Cache and Cookies and …), you need to clear its cache contents or disable them to see your changes. Also, in Elementor, please don’t forget to click on the regenerate all assets file and data in Elementor > Tools; and finally use hard-refreshing keys and recheck the issue. To refresh the page, please follow the steps explained in this link:
https://www.documate.org/automation/what-is-a-hard-refresh-how-to-do-a-hard-refresh-in-any-browser/
https://www.usmobile.com/blog/how-to-do-a-hard-refresh-on-your-browser/
To clear cookies, use this icon: https://postimg.cc/0rtp7SS9.

Summary:
Win: Ctrl+Shift+R
Mac: Shift+Command+R

Clearing all caches depends on the cache at the ISP, which might take time. Alternatively, you can check it on a device that you haven’t used to access your website recently or check your website on a guest browser.

I hope it helps,
Best Regards