I've entered 'MyBanner' because that is what I'm centering. Essentially you are adding an ID to your HTML gadget so when you enter your CSS code, it knows what gadget to alter. For instance, if you are wanting to move your profile picture, you could enter 'profilepicture'. You could name it 'rainbowsandsunshine' if you really wanted. It doesn't matter, you're just giving this element a unique identifier.
Then you are going back to your 'Template' and then back to 'Customize' and this time click 'Advanced'. Scroll down until you see 'Add CSS'.
Now you want to add your CSS code telling it where you want your specific gadget you just named.
Again, I am using 'MyBanner' because that's what I'm focusing on. You will enter whatever name you gave your gadget in the last step. Be sure to include the # before your gadget's name. Where you see '-95', this is the number that changes it's position. Change this number and play around with it until it's positioned where you want your gadget. You will be able to see what your blog will look like in the window below the code. Now, go back to View Like Us to make sure everyone else is seeing what you're seeing. That's it, you're done! Boom!
As always, if you have any questions be sure to ask. I'm here to help! Happy blogging!