Yep what I posted above did exactly what I thought it would; it blacked out my my contact form.
.custom input, textrea{
background: none;
However I finally figured out what I needed to do! (looks like I need to take CSS-101)
In my custom.css file I have added this line at the end:
.custom .paypal_image { border:none; background:transparent; width:auto; }
Then I added class="paypal_image
to the HTML code inside the PayPal <form>
<input type="image" class="paypal_image" src="https://www.paypal.com/en_US/i/btn/btn_cart_LG.gif" height="26" width="120" border="0" name="submit" alt="PayPal - The safer, easier way to pay online!">
<img alt="" border="0" src="https://www.paypal.com/en_US/i/scr/pixel.gif" width="1" height="1">
</form>