Have you tried using lightningStylesheets="true" attribute in your VF page. If possible, please post your code for VF page and controller.

Thank you,
Vinay.

Hi Parantap,

Data import wizards limited standard objects, and products is not one of them. Try using Data loader tool. This is recommended by salesforce when Import wizard does not support the objects we want to work on.

https://help.salesforce.com/articleView?id=when_to_use_the_data_loader.htm&type=5

Thank you,

Vinay.

public List<Opportunity> myOpportunities {get; set;}

public pageReference cancelButton()
{
  myOpportunities = [Id, Name, ...any other fields you want... FROM Opportunity];
  return null;
}

Hi Sharmila,

Try defining list of Opportunities using  SOQL. Something like above.