How to change the Post Background Opacity?

I am having the same problem, I have a killer background image want to make the color background more transparent so it shows through, surprised there isn’t already an option to do this as this should be a basic tool… from what I have read I need some CSS which I don’t know the first thing about. Anyways if someone could help that would be great!
The site I am working on is tractorlaunch.com.

try this. change the .4 for the footer and the .9 for the page to suit your tastes. lower number is less opaque. Works best with a dark theme.
/* change bg to opaque*/

#footer-sidebar { background-color: rgba(38, 38, 38, 0.4); }

.site {
background-color: rgba(38, 38, 38, .9);
}

That changed the background of the theme but not the pages or posts backgrounds. They are still white. I need to make the page and widget backgrounds opaque.

Got it figured out:
For pages:
.post-content,.single-post-content,.post-comments,.comments-area{

background: transparent;
}

Widgets:
#secondary .widget{
background: transparent;
}

would you show us the site you are working on?

https://kersav6.freehostia.com/wordpress/