Black box around transparent Canva image & CSS code

Hey guys! So--

I purchased a template for my SQSP site from Big Cat Creative-- They're amazing and have gorgeous templates!

I use Canva constantly to design my site and when I download a transparent image and put it on my site, there is a thin black box around it I can't seem to get rid of. SQSP emails to me say that there's a custom CSS code to fix this but given that the CSS coding was already input from the BCC team when they installed my template, I'm terrified to touch it in fear of messing up the template I paid for. HELP! Suggestions!? 

Hi,

Can you share link to page where you use that? We can check problem easier