The example you CSS you just posted doesn't include any of the examples Beth sent you.
I looked at this post as an example:
http://synergeticprocess.wordpress.com/2013/02/28/hey-listen-up/
1. How do I remove the thin line under the main header.
I tested this CSS and it worked:
#main {
border-top: none;
}
To make it work for your blog, add that CSS to your Appearance → Custom Design → CSS editor and save changes.
2. How do I remove the shadow and box in our logo at the bottom of each post.
This example will work, but only if you inserted the image using this method: http://en.support.wordpress.com/images/#insert-an-image-you-have-already-uploaded (doing it that way should make it so the image gets a specific class name such as "wp-image-46"):
.site-main .entry-content img.wp-image-46 {
border: none !important;
box-shadow: none;
-webkit-box-shadow: none;
}
However, it looks like you haven't inserted the image the same way in every post, and so the HTML is different and the CSS would need to be different too. To avoid that problem, you can set a unique class name in the HTML when you add the image.
For example, if you look at the Text tab when editing the "Hey, Listen Up" post, you'll see this HTML for the logo at the bottom of the post:
<a href="http://www.synergydesign.ca"><img class="noshadow" alt="Print" src="http://synergeticprocess.files.wordpress.com/2013/02/synergydesignlogo-footer1.jpg?w=150" width="150" height="45" /></a>
See the "noshadow" class? You can use that in your CSS instead of the class Beth used which was based on the image as it was inserted into another post:
.site-main .entry-content img.noshadow {
border: none !important;
box-shadow: none;
-webkit-box-shadow: none;
}
Then you would need to make sure every image you wanted to remove the borders and shadow from had the "noshadow" class added to it in the Text tab (HTML) view.
3. How do I remove the faint yellow and orange backgrounds behind the posts and comment section?
Beth's example works for comments. If you look at the HTML for your posts, you'll also see that a background color is applied to the main post areas which have a class name of "hentry". In that case, you can simply add ".hentry" to the selector list for that CSS block to make it cover both areas:
.hentry,
#comments {
background: none;
}