Hello-
Thank you for the excellent question. You’re right that the Linx Theme uses a hard-coded background pattern and I’m sorry that’s giving you so much trouble.
Checking out your website, it looks like you may have already worked this out with the following code:
.page-template-page_home .entry-content, .post-title-hidden .site-content, .mce-content-body {
background: url(images/shadow.png) center 0 no-repeat, url(images/tea-parchment-background.jpg) repeat;
}
I recommend that you place this code into your Customize -> Advanced -> Custom JS & CSS menu, rather than directly into the theme code, but your solution looks like it’s working.
Please write back if you need any additional help!