Hello, @Kazi Sabit,
1- Actually, by default the buy now button doesn’t appear on the mobile sticky cart bar only add to cart with quantity buttons will appear and it appears fine as you can see in this image: https://prnt.sc/ozYvZePbdaGj
2- The issue is resolved now please check back to your site after clearing the browser cache. I added a custom CSS code in the theme options check the image: https://postimg.cc/v48NKdFK and here is the resulting image: https://postimg.cc/3WB6FwzG
Regards 8Themes Team.