Hello,
1) I have tried to reupload images to the main slider and banner. Saved settings and it’s ok.
2) Because you set headings color to white https://prnt.sc/1rp2k62
3) Fixed. Check now.
4) Don’t see the problem with the add to cart https://prnt.sc/1rp3mkb What product are you trying to add and get the issue.
Regards