Replace the blue image on the mini-site of Dash theme

A lot of customers are asking how to replace the default blue background image on mini-site pages in the Dash for signup theme:
To replace this image directly from the merchant panel you will have to edit the actual theme. When you are in the Theme Editor, enter the img/ directory and find the affiliates_bg.jpg file there:
Use the 'Delete image' button and 'Change image' button and save your change. Go back out of the img folder and search for custom.css file and add the following code at the end of the file and save it:
.c1_AffiliatesMainbox { background:#fff url('./img/affiliates_bg.jpg') center center no-repeat; }
If you created a new theme, do not forget to set the new theme as the default one.