Centering banner in bottom

Apologies, total WP newb here. I had some free space at the bottom of my home page so I decided to add a banner. Surprisingly, I was able to add the banner and even make it a hyperlink. However, I cannot seem to “center” the image in my space. I tried playing around with some of the margins in style.css and and bottom.php but cannot get anything to work.

My homepage is https://blenderdude.com The banner is the one for “Blendtec Total Blender” at in the green-colored space at the bottom above the footer.

Thanks in advance for any help.