How to change blog to transparent so the background can be seen

Hi, I would like to change the body of my blog to be able to see the background. I did find some help online but the result was too transparent. I want a more opaque effect, not completely transparent. I changed the code a couple of times, adding code to make it opaque and playing with the opacity number, but nothing changed the transparency effect. I’ve ended up changing it back to normal until I can figure out how to get a slight transparency effect behind the posts. It seems from the little research I’ve done that there are a lot of people wanting this effect; it’s a wonder WordPress haven’t come up with the instructions on how to easily achieve this. Hope someone can help – remember I am pretty raw at this and pretty much “monkey-see, monkey do” – which can be dangerous, I know! Thanks in advance.
I’ve included a couple of the changes I made, per advice from online help:

/* Page structure */
.site {
padding: 0 24px;
padding: 0 1.714285714rem;
/* background-color: #fff; */
background-color: opacity:0.50;;

and the other one was:

/* Page structure */
.site {
padding: 0 24px;
padding: 0 1.714285714rem;
/* background-color: #fff; */
background-color: transparent;
}