Repeating image on posts

Your theme isn’t set up the same way as that one, but something like this would achieve close to the same effect:

#content .container {
    background-image: url("path to image");
    background-repeat: repeat-y;
}

If your theme offers a custom css option, you can add that code there. If not, you can use a custom css plugin or implement a child theme.

Thanks so much for this information – I will try it.