How can I increase the product image window size in CSS?

Hi there,
I have tried to update the CSS Classes. But there are a lot of classes, Can anyone please guide me to update the CSS code? I want to increase the product image window sizes.
Here is the link, https://giftandboxnantucket.com/products/build-a-gift-box

The APP SUPPORT is not responding!

Kind regards,
Ijaz

Please follow the steps:

  • Step 1: Go to Online store > Themes > Actions > Edit code.
  • Step 2: Go to Asset > theme.css and paste this at the bottom of the file:
    #bxp-modal__content .bxp-bldr-col-md-6:first-child{
    max-width: 70%;
    flex: 0 0 70%;
    }
    #bxp-modal__content .bxp-bldr-col-md-6:last-child{
    max-width: 30%;
    flex: 0 0 30%;
    }

unfortunately, It’s Not Working.