Background not transparent on PNG image

I have been through every single setting on the pop up builder page, but for some reason, the pop up builder keeps surrounding my PNG image with a white background. How do I remove this? I am trying to pop up a doll, that I have used in the past and made in photoshop, which is transparent all around the edges, but using this plugin, it has a white background, I have even tried playing around with custom CSS.

Please help!

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