MichelleC

There are some things that CSS is great for, but there are others where it isn’t recommended. This is one of those.
If you want the logo centred in the navigation I recommend swapping to a Brine family template. There are Site Styles built in to allow this - and more besides. 
 
On the subject of CSS, check your current styles because you have some overflow currently:

Add to Home > Design > Custom CSS
.sqs-block-video img, .sqs-block-image img { border-radius: 50px; }