For best printing results, ensure all important content (text and important parts of your photos, logos, and designs) is within the safety line and that the background extends to the bleed line. A standard bleed [...]

You can, but we highly recommend you do not. Borders can come out uneven or lopsided due to our cutting/trimming process:

If you plan to submit your own design files, rather than utilizing our free online deisgn tool, please review the following specifications carefully to ensure that images print sharply, fonts display properly, and that layouts [...]

This tutorial shows you how to flatten transparencies in Adobe Illustrator. We flatten transparencies to avoid any unintended effects they may cause during the printing process. Here are the steps to follow to flatten transparency. [...]