CraigCoxson
The code:
textarea {
background-image:url(http://cdn.obsidianportal.com/assets/250567/black.jpg) !important;
}
The warning: as with all quick and dirty fixes, make sure you know what it will do. In this case, the !important tag overwrites any coding for the background-image entry on every textarea. Only an !important on page or more specific CSS entry can overwrite it.