.slider-img {
   background;none;
}

To add CSS:

• If you are using WordPress 4.7 or later, use the “Additional CSS” option in the customizer.
• If your theme has a custom CSS option, use that to add the CSS shown above.

Learn to use the Chrome Developer Tools to help you see and test changes to your CSS.

As you use a commercial theme/plugin and need support, please use their official support channel. We feel they are best equipped to support their products.

https://themeforest.net/item/phonerepair-mobile-tablet-phone-repair-shop-wp/14856217/support

Commercial products are not supported in these forums. You are their customer; I am sure they will have no problem supporting you there.

Thank u. I added the code in both, in custom css and with live preview in additional css, but is still the same..