How to change the background color of a single element

Hi!

Is it possible to create, let's say a text block, and change that single blocks background color? And what would be the code for that be?

I'm using Squarespace 7.1 if that makes a difference.

Add to Home > Design > Custom CSS

div#block-yui-12abcdsdf {background: red;}

How to find Block ID. https://chrome.google.com/webstore/detail/squarespace-collectionblo/bggpdfnccodbnmcndckmeehdjkjojkde