Webp Background Colour Thumbnails

Hi there,

On my site, I'm using the native CS cart option to activate WebP images. It's great, site loads quicker, however, i'm looking for a way to specify the background colour for my thumbnail images directly below my main image.

You can see an example in the attachment - it's currently white, but I'm looking to make it transparent.

Any idea how? My main image uses a transparent background.

You can see in the generated thumbnail it is white: https://www.trauve.com.au/images/thumbnails/147/147/detailed/21/ella-linen-shirt-42638-trauve.jpg.webp