this: <body background="https://h1.ripway.com/vaibhavbthl/Images/Ancient%20Scroll.jpg">
is not a valid way to add a background image to anything;
when you are trying to modify themes, you need to understand at least the basics of html, and css; for instance by looking into tutorials such as:
https://www.w3schools.com/
for background css:
https://www.w3schools.com/css/css_background.asp
also, when you are following the tutorial from your first post, you need to edit your post in the html mode of the editor, and not change back to the visual editor mode.
you actually need to change the structure of the code into a single line, at the beginning:
<div style="background: transparent url(https://h1.ripway.com/vaibhavbthl/Images/Ancient%20Scroll.jpg) center top no-repeat; margin: 20px auto; padding: 45px 10px 20px; width: 90%; ">
YOUR POST TEXT HERE
</div>
however, i am not sure how this would fit in with the structure of your site, and with the slider.