Need help to adjust my CSS code - css

Question

A few years ago I made some CSS code customization on my forum. Since then (probably, due to updates or some other reason), right now it doesn't show it right (the way it was). The idea is that I've got one color of a bg where there's a name of a poster and his avatar and then there's another color where there's text that he writes (verbiage of the post itself). I'm attaching the print screen on which I show what exactly do I mean.
Also I would tell what I did so far to achieve the effect (though it's not exactly right at the moment).
In file Themes/default/css/index.css (line 1921) I added this line of code:
background:url('http://idevsky.com/images/post_bg.png') repeat-y;
And also I changed the height to 0px from 11px in two places:
line 972 and line 987
You can see it if you go to:
http://idevsky.com/forum/index.php
Test account credentials:
j.smith qwerty
Then you click on John Smith (the only board) and then you go to "test" thread (the only one there).
There're 3 different colors:
1) the one where the poster name and avatar is (#dfecf5), it's the way it should be.
2) then there's one that covers the majority of post text area (#ebf3fb), it's the right color, it just doesn't spread right
3) then there's one irrelevant (wrong) color (#f0f4f7) which you can hardly see in the second post (the one that j.smith wrote) and it starts from the arrow point to the right.
print screen

Answer 1

Just remove your image and give it a background color also give your poster class a background color.
.post_wrapper {
background: white;
}
.poster {
background: aliceblue;
}

Answer 2

Search index.css and you change the background-color of .windowbg and .windowbg2 in the CSS file to #ebf3fb as the following:
.windowbg, #preview_body {[enter image description here][1]
color: #000;
background-color: #ebf3fb;
}
.windowbg2 {
color: #000;
background-color: #ebf3fb;
}
Check out this picture to help you find the code:
http://i.stack.imgur.com/MfJaB.png