-2. Create the banner image. Some guidelines:
- * Image should be 350px wide (exactly) x 350px tall (or shorter).
- * Use a standard web image format (.gif, .jpg, .png)
- * Note that a close 'X' button will be drawn over the top right 60x60px corner of the banner, so please do not put anything important in that space.
+2. Create the banner image. The image needs to:
+ * be exactly 350px wide and at most 350px tall,
+ * be in PNG format,
+ * have nothing important in the top-right 60x60px corner of the banner which has a close 'X' button overlayed, and
+ * have sufficient visual contrast with the colours #cccccc and #999999 so the 'X' can be seen.