Fabric.js cannot have the background of a canvas transparent

Question

I would like to have the canvas (see image) to have a background (around the gabarit) to look like this:

I have tested to save the canvas with background color set to null and background image set to null, but it's always white.

The URL of the site is https://linkmx.fr/accueil/307-plaque-downhill-odi-100-perso.html then you have to click on "Personnalisez"

user_7693185 · Answer

You can set the canvas background to transparent like this:

canvas.set('backgroundColor', 'transparent').requestRenderAll();