The Adventure Journal theme uses the following background image for the main content area. The image has the shadows build into it:
http://s2.wp.com/wp-content/themes/pub/adventure-journal/images/mp-sprite-content-bg.png
What you could do is download that image, create a new image without shadows on the side, upload the new image to your media library, and use CSS to replace the image like this:
#wrapper-content {
background: url(YOUR_IMAGE_URL) 3px 0 repeat-y;
}
Replace YOUR_IMAGE_URL with the link to your image.
An alternative would be to set the background to a solid color instead like this:
#wrapper-content,
#wrapper-top {
background: #fcf5f5;
}
#page-curl {
display: none;
}
Adjust the color code as necessary.
You could add interest to a solid color background by making the border radius for the top left and right different:
#wrapper-top {
padding-top: 8px;
-webkit-border-top-left-radius: 15px;
-webkit-border-top-right-radius: 15px;
-moz-border-radius-topleft: 15px;
-moz-border-radius-topright: 15px;
border-top-left-radius: 15px;
border-top-right-radius: 15px;
}