I have a fabirc.js canvas. Now i want to add an active area in it, in which the fabric.js elements should be. If the user move they outside this area, he get the message, that the element is outside this area.

Here is an image, where you can see what i mean: https://ibb.co/Hn5qC8b. On this picture you can see in the center a square which have no background-color. This is the area, which i want to add into the fabric.js canvas.

Do anyone have an idea how i can add this active area into the fabric.js canvas?