Use color or image as page background

Replace background with color

Paste this code in the "Customizations" window:

.rendered-page {
  background-color: red;
}

*You may also be interested in using gradient backgrounds, if yes, we have a manual for that too: https://brick.do/AqXXRPymKaLN

Paste this code in the "Customizations" window:

.rendered-page {
  background-image: url("YOUR_URL");
  background-size: cover;
}