Solution:
Without more information (some HTML to go with it) or a webpage you are having trouble with, it is very hard to understand what you are trying to accomplish.
I would try something like this, as it sounds like you are trying to have the background image repeat.
hero {
background: url(‘/wp-content/themes/bootstrap2wordpress/assets/img/hero-bg.jpg’) repeat;
}
https://www.w3schools.com/cssref/css3_pr_background.asp