You could use CSS generated content. This will mean editing your HTML - to remove the arrow. Essentially you're creating a pseudo-element that sits in front of the link, and you can style it however you like, e.g.
a.back:before {
content: "\2190 "; /* Unicode equivalent of ← */
display: inline-block;
padding: 5px;
background-color: aqua;
}
On the downside this won't work in IE 6 or 7. You might be able to work around that with some targeted javascript.
If you don't want to edit your HTML, you could give :first-letter
a try. It only works on block-level elements, so you'll need to work accordingly, e.g.
a.back {
display: inline-block;
}
a.back:first-letter {
background-color: aqua;
padding: 5px;
}
I've had trouble getting this to display consistently cross-browser though. IE8 and FF3.6 do rather different things with the code.