Forum:Redirect Arrow Replacement

The redirect arrow graphic was made with the assumption of it being displayed against a white background. And rather than fade into transparency, the black fades to white and cuts off. An example can be seen here.

So, I have made a graphic replacement for it, but have yet to upload it. What coding should I put in what CSS page for it to change? (Substitute "picurlgoeshere" or something for the picture URL.)